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CUClickers / iClickers - FAQ

General FAQ

What does a student response system do?

According to an Educause document titled 7 Things You Should Know About Clickers, "The system allows for active participation by all students and provides immediate feedback to the instructor-and the students-about any confusion or misunderstandings of the material being presented."

How does it work?

The instructor's receiver and the students' remotes communicate using radio frequency (RF) technology. Some earlier clicker systems used on campus utilized infrared (IR) technology. While IR clicker systems require line-of-sight between the remotes and the receivers, necessitating a fairly involved receiver installation, RF remotes only need to be in the general vicinity of a receiver (usually 200-300 feet).

RF systems do require that remotes and receivers are configured to use the same communication frequency. Frequency settings are an important aspect of the system, and receivers that are in close proximity to one another should be configured to use different frequencies. If they use the same frequency, remotes may send their answers to the wrong receiver and "pollute" that receiver's result set.

How can CUClickers be incorporated into my class?

There are many pedagogical uses for a student response system. Occasionally, OIT sponsors training sessions that cover classroom use. Check out the First Day of Class slides for iClicker Cloud to assist students getting started with iClicker as well as the Instructors technological resources page, which has documents provided by CU Boulder faculty.

Why did OIT choose iClicker to be the hardware and software for the CUClickers service?

A faculty committee evaluated several clicker systems and found iClicker to be the system of choice. A subsequent online forum also indicated that iClicker is favored by the majority of those who participated in the discussion. Based on this input, the campus chose to build CUClickers around the iClicker system. The iClicker Student App (formerly iClicker Reef) and Cloud were selected based on their compatibility with the iClicker remotes and bases in use on campus already.

How do I get a CUClickers receiver?
  • Receivers can be found in the media cabinet of most classrooms across campus. These media cabinets can be opened with a master key, provided by the IT Service Center.
    • View the list of classrooms with receivers.
    • Learn more about media cabinets and keys.
  • If your room does not have a receiver, you may request an instructor kit from the IT Service Center.
What is the difference between CUClickers and iClicker?

CUClickers is the name of the OIT service that utilizes the iClicker system. While iClicker is certainly at the center of the service, CUClickers includes centralized support, faculty training, integration with CUConnect, and other features.

What is the difference between iClicker Student and iClicker Cloud?

iClicker Cloud is the software faculty use to poll students and manage clicker grades. The iClicker Student App is the software students can use to review clicker questions and their answers, as well as to vote when in a remote learning environment.

Where can iClicker remotes be purchased?

Instructors and students can purchase iClicker remotes at the CU Bookstore. Furthermore, a limited number of iClickers can be checked out from the technology desk at Norlin Commons.

Where do students register iClicker remotes?

Students need to register remotes in iClicker. Learn how using the Add an iClicker Remote ID to a Student Account tutorial.

Can I create manual rosters and/or roll calls?

Yes. Learn more by visiting the iClicker Instructors page and downloading the comprehensive user guides.

How can I help my students succeed using iClicker?

First, communicate in multiple ways that your students will be required to use iClicker Student. Try using Canvas Announcements, email, and assignment descriptions, and make it clear to your students what the exam rules are. Refer students to the Student guide for help. Also, practice in class, so your students can confirm that the app is working correctly on their computer or mobile device.

Do Students have to pay for iClicker Student App?

Students never have to pay to use iClicker Student with an iClicker remote. That service is free. For the 2020-2021 Academic year, the subscription fee to use the iClicker Student App on a mobile device has been waived.

When can I use iClicker on my phone, tablet, or laptop?

You can use iClicker on your mobile device when you are in a remote learning environment.  When you are in the classroom, you should use an iClicker remote (aka, a clicker) because of the potential for wireless connectivity issues.

Can students use their phones to vote in class?

No. Students should not use mobile devices for in-classroom polling due to the potential for wireless issues.

Hardware Setup

How do I set up a CUClickers system?

Connect the i>clicker receiver to your computer with the included USB cable. The receiver should immediately power itself on. (Note: the receiver draws power from the computer’s USB port. Please make sure the computer has sufficient battery power or is plugged in.)

The computer would typically be connected to a data projector to allow students to see questions and responses. However, the system functions without this connection.

What kind of batteries does the iClicker remote take? How do I change them?

The iClicker remote takes two AAA batteries. To remove the battery cover, push down the small tab next to the battery compartment. 

What do I do if the spring in the battery compartment wears out or becomes loose?

The CU Bookstore has replacement springs available, or use a tweezer to readjust the spring. 

How do I turn on my iClicker remote?

Once you remove your iClicker from its packaging, you will need to pull the tab on the back of it to activate the batteries. On the front of your clicker you will notice there are 6 options: A, B, C, D, E, and On/Off. The On/Off button is what you choose to both turn it on (resulting in a sold green light by the “Power” indicator at the top of your clicker) and off (removing the solid green light).

How do students register their iClicker remote?

Students need to create an iClicker account, and link their clicker to that account.  For hybrid learning, students can use iClicker Student App on their mobile device or computer. For in-person learning, students should use an iClicker remote.

Software Setup

What software do I need to run the CUClickers system?

To run the CUClickers system in a classroom, you need the software folder containing the iClicker program and other assorted files. (You’ll only need to run the iClicker application.) Download iClicker.

How do I get the software?

You can get the CU Boulder specific software at no cost. You will only be downloading a .zip file that once unzipped is a folder with the iClicker application. Learn more:

What operating systems work with CUClickers?

For Macintosh, instructors must run macOS 10.12 (Sierra) or higher. The Windows software works on Windows 7 and higher. iClicker also supports Linux ubuntu 12.04-LTS 64bit, though OIT does not. 

How do I run the software?

Double-click on the iClicker application on a Mac, or i>clicker.exe on a Windows computer, then choose either Start Session or Resume Last Session.

How do I load a class roster?
Does the update process erase my session data?

It shouldn’t, but it is wise to back up your data. When backing up your data, please be aware of FERPA guidelines and of the Office of Information Security recommendations that can help keep data safe.

What does the iClicker software look like when it runs?

Once a session is started, the iClicker software runs by default as a very small toolbar with few options in the upper-left corner of the screen. This is so it can run in front of other presentation materials, such as PowerPoint slides, without getting in the way. However, it's also possible to use the small toolbar to bring up other pop-up displays, such as a chart of current results, which do take up more space.

How do I add questions to the software?

You don’t. The iClicker program only controls the reader and collecting student responses. It doesn’t have a way to present questions or polls. Since the main iClicker window is just a small toolbar, though, it’s designed to be used with another presentation method, such as PowerPoint.

Are there any major differences between the Mac and PC versions of the software?

Not really, though be sure to run the right version for the operating system.

Instructional Use Questions

Are clickers good for small classes, or only for large lecture?

As one of our instructors (Doug Duncan) says, “Even in a class of 5, students can hide.” Thus, we consider the general pedagogical technique – asking students to discuss challenging questions with one another – to be valuable in any class size. Additionally, a recent dissertation (by Angel Hoekstra at CU Boulder) shows that the largest impact of the use of clickers is in the whole-class discussion following the individual voting. This discussion can be a part of a class of any size. In an extremely small class, the clicker technology may be redundant. However, in classes of at least 25-30 students, we find that the addition of clicker technology can be a valuable way to allow students to check their understanding and break up a lecture.

Doug Duncan (CU Boulder) says: “In my science seminar class of 10 students they didn't speak out as much as they should have, because they overestimated what they knew. If one student did something on the white board they often thought, "yes, that's what I would have answered." But on an exam they weren't as good as they thought. For that class I adopted "clicker methods" without the clickers. That is, I often asked questions, had EVERYONE write the answer on paper, exchange the papers and critique each other, THEN have class discussion. Exam scores went up 15%.”

Adapted from iClicker discussion forums.

Do clickers work in upper level courses or are they only good for introductory?

We have several examples of instructors who began using clickers in large introductory courses and then tried them in smaller upper level and even graduate courses. They are very enthusiastic about the results, and students in upper level clicker courses strongly supported this use on our surveys. Additionally, a growing number of studies on instruction in the upper-division indicate that the effective use of clickers create learning gains for students in those courses. Even in the more intimate settings of an upper-division course, students can still have trouble speaking up. Clickers can be used to help students identify where they are struggling, and show students that they are not alone in these difficulties. Clickers can also help elicit discussion points that don’t come out as easily without the support of clickers. Additionally, they can give the instructor insight as to where the students are struggling in the class – which can sometimes lead to surprises! Of course, students are more sophisticated learners at the upper-division, but clickers can be used to address particularly complex ideas that it would be difficult for students to learn on their own from the book.

Adapted from Connexions module by UBC Carl Wieman Science Education Initiative, CU Science Education Initiative: http://cnx.org/content/m26443/1.1/

Do students like clickers?

Reflecting on research that has been done on clickers in the introductory classes, the research consensus seems to be that students really like clickers when they are being used as a *learning tool*! They don't like clickers if they think they are just being used for attendance or for testing. So explaining to students *why* you are using clickers and how it will help their learning, and focusing on using them as a tool in increase active learning and student-student discussion will almost certainly lead to student enjoyment of clickers.

After years of good experiences using clickers in the introductory courses, we have started using clickers in our upper-division college physics courses (ranging from 10-50 students). We've surveyed 16 different courses, and the signal is clear - 82% of these junior and senior students find lecture with clickers MORE useful then pure lecture with only about 6% voting to drop clickers. When we look at what they say about *why* clickers help their learning, we find that these students have a good sense of what helps them learn and be active in their learning. They say things like: lets me monitor and check my understanding, gives me time to think and digest the information, allows me to try applying what we just learned, keeps the teacher in touch with the students, allows me to hear other student ideas, allows me to talk through my own ideas, keeps me engaged in lecture, prevents me from getting lost, etc.

We ask students what their recommendations were for faculty looking to use clickers. They recommend about 3-4 questions interspersed throughout class (50 min) and allowing and encouraging student-student discussions during the clicker questions (80%). In terms of questions, they had a strong preference for challenging conceptual questions (as opposed to plug/chug or recall questions) - these students want to be challenged and think during the questions. But its good to have some questions that are challenging and generate good discussion among the students but still have a pretty high response rate (80% or so) - too many questions where a large number get it wrong can be a bit discouraging for the students.

We didn't expect such an overwhelmingly positive response from these upper-level students, but that's what we found. As a result, there have been more and more of our faculty using clickers in upper division courses (14 different faculty so far).

Adapted from iClicker discussion forums response by Kathy Perkins.

Don’t “strong” students just give “weak” students the answer if there is discussion?

Research suggests that this isn’t a great concern, and that both “strong” and “weak” students benefit from interacting in peer discussion.   One study (Smith et al., Science, 2009) found that even when nobody in the group knew the right answer, they were able to put together the right answer through discussion.

However, another study has suggested that the way credit is given for answering questions can impact whether the right answer spreads through class from the strong students to the weak students. In a class with “low stakes” grading (equal credit for any response, with questions counting 12.5% of overall grade), peer discussion was more balanced, with both students in a pair contributing equally to discussion and more likely to vote differently. In contrast, a class with “high stakes” grading (incorrect responses earning 1/3rd the credit earned by a correct response, questions counting 20% of total grade), students earning higher grades dominated peer discussion, and both students in a discussion pair more often voted the same. In a small study we did in a different course, we found the correlation between students’ clicker question answers and their course grade was surprisingly low, indicating that as students were first learning new material, there was little distinction between “weak” and “strong” students. No matter what the achievement level of the student is, encouraging them to articulate their thinking is beneficial.

Adapted from Connexions module by UBC Carl Wieman Science Education Initiative, CU Science Education Initiative:  http://cnx.org/content/m26443/1.1/

How do I facilitate a productive wrap-up discussion at the end of a clicker question?

It is important to discuss the answers to the question at the end of the process. Even if most of the students got the answer right, a quick discussion of why the right answer is right, and why the wrong answers are wrong is valuable to students to help clarify the reasoning behind the question and clear up lingering misconceptions.

We recommend waiting to show the histogram of student responses until after class discussion. Showing the histogram too early results in students thinking that they know the answer (that is, if there is a clear majority vote), and thus less willingness to engage in discussion. We find that asking several students to share their reasoning about each answer choice helps to bring common ideas to the table so that they can be discussed as a class. A helpful wording that we use to make this less intimidating is to ask students to explain the reasoning behind different answers even if they didn’t vote for that answer: “Even if you didn’t vote for A, why might someone have chosen A? What is tempting about A?” When students try to explain why they think a certain answer (e.g., “B”) is right, halt their explanation – you want to hear the reasoning behind the other answer, even if they don’t believe it. This emphasizes the importance of reasoning in the questions. A focus on reasoning can also make the peer discussions (before the whole-class discussion) more productive, since students know that they will be called on to share their reasons.

How do I get students to get back on task after a clicker question, and stop talking?

A good signal that students are finishing their discussions is when the voting gets up towards 75% of the class. Having an established signal for when discussion needs to end works well, such as a gong tone, whistle, or switching off the lights.

 Adapted from Connexions module by UBC Carl Wieman Science Education Initiative, CU Science Education Initiative:  http://cnx.org/content/m26443/1.1/

How do I promote discussion between students?

Achieving good discussion between students is often the hardest but most important part to maximizing the benefit of clickers. This is a change in the culture of the class, and so you should not expect it to happen automatically. You should not give up if it takes a little while to develop, and you should actively encourage it, and explain and model scientific discourse for them.   

First, help students buy-in to the importance of discussion by making it clear why you are using this technique – that it is to help them learn the material.  After all, discussing questions with one’s neighbors takes extra work on the part of the student, and so it needs to be clear that it is worth their while.   Instructors can promote this by explicitly informing students of what they expect and why the interactive/discussion approach helps students learn. This should be done repeatedly during the term as opposed to just at the beginning. To find a video with an example speech you might give to students go to http://STEMvideos.colorado.edu.

Also, on the first day and a couple of subsequent days, encourage the students to learn the names and shake hands with everyone around them (in front and behind included). Also giving the students permission to ask names they’ve forgotten can be surprisingly helpful. We may not be able to learn the names of the whole class, but students appreciate knowing someone knows their name.

Find ways to remove the social barriers to discussing content with one’s neighbors. Some instructors make it clear that if they don’t see students actively discussing, then they will be asked first to share their reasoning with the class. Thus, reluctant students have an excuse to talk with their neighbors (“Hey man, guess we better talk so we don’t get called on.”).

Students also need to know that the results of their discussions will be used later.  We recommend that you also tell students that you’ll be asking them to share their reasoning about the answer so they should discuss it, and then have them share their reasoning at least some of the time in the follow-up whole class discussion. Students need to feel that the classroom is a safe place to discuss questions, and everyone can potentially be wrong without consequences.

Some techniques for directly encouraging discussion are to require groups to submit consensus votes on a question. Calling on students to ask them what reason their group gave for why an answer is correct or incorrect can also help. Students find it less threatening to offer the reasoning for an answer the answer is seen as coming from the group rather than them, individually. If possible, it’s good to also require students to give reasons for answers on homework and exam answers. 

 Adapted from Connexions module by UBC Carl Wieman Science Education Initiative, CU Science Education Initiative: http://cnx.org/content/m26443/1.1/

How do I respond if technical problems arise during class?

Reassure students that technical problems in no way impact any grading scheme you have implemented. Then pose the question anyway and have discussions as originally planned, and ask for the show-of-hands approach to answering. Results can be tallied (even if roughly) on paper, the blackboard, or an overhead projector.

 Adapted from Connexions module by UBC Carl Wieman Science Education Initiative, CU Science Education Initiative:  http://cnx.org/content/m26443/1.1/

How do I write a good clicker question?

First, it is important to use questions that target key, important ideas in the course.  Often, students will walk out the door with a firmer grasp of the material in the clicker questions than of other material – so the clicker questions should be focused on the most important ideas, rather than peripheral topics. Additionally, the clicker questions frame for students what you feel is important in the course, and will often guide what they think is important to study for the exam. 

It is important to use questions of a mixture of difficulty.  Students will learn the most from challenging questions, maximizing the benefit of the time spent on them.  However, we also find that students benefit from review of basic concepts, and their confidence is improved when they see that they are successful at answering some questions. 

One challenge is to write tempting distractors – the “wrong” answer choices.  If a student can easily pick out the right answer among the choices, the question will generate less discussion and be less useful in student learning.  Good distractors can often be found by looking over student responses to open-ended questions, such as on homework or exams.  Some instructors might give a question as an open-ended question to the class first, and generate distractors from student responses.  Research literature on common student misconceptions is also a helpful place to start.

While clear wording on a question is important, sometimes deliberately ambiguous questions with more than one right answer can be useful in generating rich discussion.  A “bad” question can illustrate that the correct answer depends on the assumptions not presented explicitly in the question, for example. 

It’s always easier to start with someone else’s questions – whether you use them verbatim, or modify them for your purposes. So chat with other instructors, or look for good questions on the web.

How many clicker questions should I give in a lecture?

Most instructors find that between three and six questions in a 50-minute class period works well.   This matches with studies on student preferences.  These should be distributed throughout the lecture rather than all clumped at beginning or end. In general, students’ attention often starts waning after about 10 minutes of straight lecturing, so a good rule of thumb is to ask a clicker question every 10 minutes.  Avoid going too far the other way – all clicker questions, all the time is not necessarily better (and in our experience has resulted in lower learning gains and poor student evaluations). If one is using other active learning techniques in a lecture period, the number of clicker questions will likely be lower. For a review before an exam, it can often be more effective to fill the lecture period with many clicker questions rather than using other types of review.

 Adapted from Connexions module by UBC Carl Wieman Science Education Initiative, CU Science Education Initiative: http://cnx.org/content/m26443/1.1/

How much do clickers cost?

Clickers cost students $40 purchase to new. Often, they can be resold at the end of the term. As CU has a set brand of clicker, students may use them in several courses.

How much time should I give students to answer a clicker question?

This depends greatly on the type and difficulty of the question: in most cases, it takes students between 30 seconds and a minute to process a question and be ready to answer individually or discuss. It then takes a few (1-4) minutes for productive discussion. The level of student discussion and the number of votes in is a good guide as to when to move on. When ~3/4 of the students have responded it is often a good time to announce end is near, then sound warning gong, count down out loud, or turn lights out to indicate that discussion should stop and students should “click in”. Instructors who decide when to end the polling based on the discussion around them often wait too long. While discussion around them will continue to focus on the question, in the rest of the room discussion has often moved on to non-class-related topics, making it harder to pull students back to class material. It is useful to poll the class after several weeks to see if they feel you are giving them too little or too much time. Using the timer in the countdown mode available with most clicker system software is usually distracting to students and instructors and can limit discussion. It is better to set the timer to the maximum count down duration or in count up mode, and then just stop the question manually when you think it appropriate.

Adapted from Connexions module by UBC Carl Wieman Science Education Initiative, CU Science Education Initiative: http://cnx.org/content/m26443/1.1/

How should clicker questions be graded?

Most instructors make clicker questions a portion of the total course grade; between a few % and 15% is common, although some advocate for using extra-credit only (such that clicker points can only help count against poor exam scores, up to a few % of the grade). The important consideration is to make sure that students do not feel that the clicker question grading is “high stakes”, as any stress about getting the right answer tends to shut down discussion so that it’s less productive. 

The two most common grading schemes used are giving equal credit for correct and incorrect responses (participation only), and giving greater credit for correct than incorrect responses.   Another approach is to give participation credit only most of the time, but occasionally grade individual questions for correct responses. Giving credit only for correct responses is not recommended as it distorts the discussion and student response strategies in undesirable directions, and it limits the type of question that can be asked. For example, you cannot ask questions with multiple justifiable answers; yet such questions can generate the most educationally productive discussions. Similarly, not having clicker questions count for any credit is not recommended. This sends the message that questions and answers are not important, and students will not take them seriously. Although student responses will vary, our observations suggest the specific grading policies do not make very much difference to students as long as one avoids the extremes that result in undesirable outcomes listed above. As long as there are consistent implicit messages from the instructor that the questions matter, students seem to take the questions reasonably seriously.

Regardless of grading scheme, some clicker questions should NOT be graded for the “correct” response but are very useful in promoting discussion, student learning, and instructor and student feedback. Examples of such questions are those with more than one potentially correct response, and those intended to elicit student misconceptions or students’ prior knowledge. We also highly recommend that whatever grading policy is used, a certain number (2-3) of “free” days are allowed. These are days for which the student will get credit even if there are no clicker responses recorded for them. This greatly reduces the time student and instructor need to spend dealing with complaints/excuses about clicker not working, being forgotten, missing class due to any number of catastrophic events beyond students control, etc. An alternative that is similar in concept is to set a certain percentage of questions students need to answer, such as 80 or 90%, and once above that threshold they receive “maximum clicker credit”. We have also seen that when clickers count for more than 15% of the grade, the amount of time spent dealing with student concerns about being sure they receive credit for clicker responses can get annoying. Finally we recommend that at the beginning of the course you should very clearly announce that use of another person’s clicker, or having someone use your clicker, is considered cheating with the same policies applying as would be the case for turning in illicit written work.

 Adapted from Connexions module by UBC Carl Wieman Science Education Initiative, CU Science Education Initiative:  http://cnx.org/content/m26443/1.1/

Should I post answers to clicker questions after class or not?

There are varying opinions about this and no data that indicates one way or another. However one study shows that when people have the answer explained to them after they have thought hard about how to answer the question, they learn a large amount from the explanation. On the basis of that research, our inclination is that it is probably better to post the answers.

Adapted from Connexions module by UBC Carl Wieman Science Education Initiative, CU Science Education Initiative:  http://cnx.org/content/m26443/1.1/

Will there be student resistance and if so, how do I deal with it?

Some students will probably resist the change in classroom climate from a passive to a more active environment, particularly as it penalizes absences and requires more effort. Most respond well if the instructor explicitly (and repeatedly!) talks with the class about the purpose of using clickers interactively, and emphasizes the positive results seen in other classes and education research.   An example speech to students can be found at http://STEMvideos.colorado.edu.

The implicit signals that an instructor sends are also very important. When the clicker responses show students do not understand something, revising the lecture plan to examine their difficulties and address them, rather than ignoring this sends a very positive signal. Requiring students to spend money on clickers and then using them only once or twice per class to answer very simple questions sends a very different signal and can generate considerable student unhappiness.

We have done extensive surveys of students in classes that use clickers. In those classes where the clickers are used in a manner at all close to what we recommend, the students overwhelmingly say they contribute to their learning and recommend they be used. It helps both learning and attitudes if you ensure that the clicker questions, homework, and exam questions indicate in a consistent manner what is important and what the expectations and standards are for the course. There can be a few very vocal students who strongly oppose clickers, but our surveys have shown that when clickers are used well, this view is never shared by more than a small minority. If they are troublesome, their complaints can be reduced by surveying the class to show that they are a small minority, rather than representing the sentiment of all (as they usually assume). Also, although most students say they like using clickers, even those who do not often still recognize their value. In the words of one such student we interviewed, “Using clickers is like broccoli – I don’t like it, but it’s good for me.”

Finally, the most effective way to eliminate student resistance ultimately is simply to use clickers to make the classroom an extremely stimulating place where students are highly engaged and learning a great deal.   As one instructor (Jenny Knight, CU Boulder) says, “When students are allowed to discuss a difficult question with each other and actually end up understanding it, it's a powerful motivator for continuing that behavior.”

 Adapted from Connexions module by UBC Carl Wieman Science Education Initiative, CU Science Education Initiative: http://cnx.org/content/m26443/1.1/

Won’t I lose control of the class if I let them talk so freely?

This is not as big a concern in practice as it is usually feared to be. There certainly is less rigid control of the class, but students also see the class as more supportive of their learning, and so they are more on your side from the beginning. It is helpful to lay out some ground rules clearly. Along with the reasons for having clicker questions and discussion, make it clear that discussion is supposed to be limited to the subject material (even though it will not always be), and that when you have signaled it is time for discussion to stop, they should do so, and any questions remaining at that time should be directed at you. As the term progresses and students get to know each other better and become more comfortable talking to each other, it usually does get more difficult to cut off discussion. Training students from the beginning to respond to some signal like a gong or lights flashing markedly reduces the difficulties and is normally adequate. If just a few students continue to talk, ask them directly in front of the class in a non-confrontational way, if they have a question. If they are discussing non-class related material, that will quiet them then and in the future. If they are discussing the class material, which is more typical, they will ask a question which you can treat like a regular question, and still send the message clearly that they were disruptive. It is unlikely, but not impossible that you may have an exceptionally unruly class where even these steps are not sufficient to quiet them down. (It is not clear whether such classes are made worse or better with clickers.) A reasonable approach we have seen for that case is, if class is not quiet after the gong/signal, simply stand there looking at them and wait. If they continue to talk, make it clear that students will be responsible for material not covered because of the time you spent waiting for class to quiet down, and then when there are subsequent disruptions, just continue to wait them out and rely on student peer pressure to deal with the noisy students.

 Adapted from Connexions module by UBC Carl Wieman Science Education Initiative, CU Science Education Initiative: http://cnx.org/content/m26443/1.1/