I learned a very simple, powerful technique for engaging students’ interest, sparking intense classroom discussions, and guiding students how to think like a physicist from the book Peer Instruction  by Eric Mazur. What’s more, if you use this technique in AP Physics you’ll be incorporating a version of scientific argumentation into your instruction, something the College Board says we must be doing in AP Physics.

PI_coverIt’s a skinny volume, but it does contain a description of the Peer Instruction method, a discussion of the results of using PI, “Climate Setting” tools (techniques for getting students to buy in to inquiry) and ConcepTests for using PI in an introductory physics class.  There is good advice in here, but I will get you started using this technique right here.

The Peer Instruction technique is fairly simple to describe and has been discussed in many places (see here, and here, for example). This post is an outline of how I use this technique, with some tips from my experiences with high school students.

Step 1. Present to students an interesting multiple choice, conceptual question.


Paul Hewitt’s Next-Time Questions contain many great examples (the link takes you to Arbor Scientific’s website where you can download all of them; or, send me an email and I can send you a link to my Google Drive folder of them all). In the example above, students would vote  (A) for 100 N, (B) for 200 N, (C) for Zero N.  I usually project the question. If you are a non-physics teacher reading this post, I can assure you that physics students will get into a very intense discussion about the question above.  

Step 2. Students silently read the question, and the teacher collects the anonymous responses.

My current favorite approach for gathering the responses is Plickers (“paper clickers”). Plickers are free, and fast. Students are assigned a card with a number and a pattern on it. They vote by holding up the card in one of four possible orientations, while a phone or tablet scans the room. They can change their answer on the fly, and the website records their responses. This usually takes only about 2 minutes, including scanning the plickers.


image from

Other high-tech methods include socrative, polleverywhere,  or dedicated remote answering systems (“clickers”).

Low-tech approaches include students voting with a stack of colored plastic cups, colored post-it notes, colored index cards, or a show of hands. These are not as good, because they are not anonymous. Some students will hesitate to vote, or just as bad, copy their neighbor’s votes. You want everybody voting their own ideas so you have the option of discussing all ideas!  

Step 3. The class views the first graph of responses.

A good question will have some respondents on every (or nearly every) choice. For the plickers website,  I have created generic (no text, no image) 2, 3, and 4-choice questions that I use over and over again, rather than typing the question text into the plickers library. The graph after responses are collected from looks like this:


Notice the vote with plickers is anonymous. I can’t stress enough how much this improves discussions. If the vote is by a show of hands, for instance, watch your students and you will see them hesitate until others have voted, or change their vote based on what their neighbors are doing. This is not what you want! You want all ideas represented in the discussion. I either place my phone under the document camera, or switch to the Plickers website “Live View” to display the graph. If I have to use the low-tech approach, I always sketch the bar graph of the responses I see on the board. This step takes about 30 seconds.

Step 4. Students discuss their own answers and the first class graph with their neighbors.

This takes several minutes on most questions, and  longer on a tough question or ambiguous question. Tell your students they must use physics to convince their neighbors what the right answer is. This is where the real power of the approach comes in. Everybody (hopefully) has committed to an answer and (again hopefully) has something to discuss. Looking at the graph is a powerful moment where they realize there are multiple ideas out there. You want them to discuss. Even discussing a guess is likely to be better than just listening to other people. Make sure everybody talks physics during this time.  The teacher roams and discusses with various groups. This is your opportunity to ask probing questions, force students to defend their reasoning, make sure everybody is engaging in the argumentation. Move quickly and check in with everybody you can. Help guide their discussion by asking “interesting” questions when they are stuck. This will also help you gain a sense of which groups to call on for Step 7. You may want groups to explain both correct and incorrect reasoning. It is important not only that students understand what makes a correct answer correct, but what makes an incorrect answer incorrect.

Step 5. Students answer again, after agreeing with their neighbors on an answer.

I command “Hold up your card for your second answer, and you better be prepared to defend your group’s answer!” This takes another 30 seconds.

Step 6. The class views a graph of the second set of responses.

Really good discussions in Step 4 may lead to nearly everybody switching to the best answer. This doesn’t happen every time. Sometimes they nearly all switch to what is not the best answer! That is also an opportunity for a good discussion. If the responses are still dispersed, you can decide, based on the quality of the discussions in the groups, to have them discuss again, and vote again. This might be a point where you provide a strong hint. For instance, in discussing the Paul Hewitt question above, a lot of students might decide that the best answer is 200 N. If this is the case, I might say to the class “If the tension is 200 N, do the masses remain at rest? Discuss again, and we’ll vote again!”

Step 7. A whole-class discussion on the final set of responses, with the goal that the class decides what is the best answer.

Have some student or students explain the reasoning for every choice, if you feel you have time. If time is short, or the discussion is dragging, you may quickly explain to the class what you heard from the groups about some choices. For instance, I might say “I heard that everybody excluded Zero newtons as the answer because everybody was sure you could feel some tension in the string, so let’s not discuss that one.” I try to get the students to reach consensus, without needing me to tell them the answer. A representative speaker is called on to defend their answer, and they are encouraged to engage in some (respectful) back-and-forth about what is the best reasoning. I try my hardest to stay out of the discussions as much as I can, interjecting only when I feel it is necessary. At the end, I try to never give up an answer, but I will say “It’s time to move on” when I feel that no more discussion is necessary. At this point they may demand an answer, but I repeat “I’m ready to move on.” Some kids really want me to explain the answer to them again, but what’s the point? They’ve already heard the answer.  If a student doesn’t get it, usually another student will say to them “Whatever we last said was right, or he wouldn’t be ready to finish.”

If a student asks, I would take the time (or have a student take the time) to summarize the reasoning we agreed upon by writing it on the whiteboard. But I don’t often initiate this. In my mind the discussion is the goal, not memorizing a solution.

I never grade these discussions for accuracy,  although I often keep track of who contributes to the discussion using ClassDojo.

Peer Instruction Links

Wikipedia page



YouTube video of Peer Instruction in use




YouTube video with Eric Mazur talking about PI

Peer Instruction blog

Peer Instruction network (nothing much there, yet)

A paper on Peer Instruction in Calculus

The Amazon page for the book

About marcreif

I live and teach high school physics in the town I was born in, Fayetteville, Arkansas. My professional interests include modeling instruction and Advanced Placement courses. I also work as a College Board Workshop Consultant, which means I lead Pre-AP and AP Science Teacher workshops. Lately I've also been leading a fair amount of student review sessions for the National Math and Science Initiative. I have a website for students ( and another for AP Summer Institute participants ( I tweet infrequently (@marcreif).
This entry was posted in Uncategorized. Bookmark the permalink.


  1. Pingback: Peer Instruction Online Update | fysicsfool

Leave a Reply

Fill in your details below or click an icon to log in: Logo

You are commenting using your account. Log Out /  Change )

Google photo

You are commenting using your Google account. Log Out /  Change )

Twitter picture

You are commenting using your Twitter account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )

Connecting to %s

This site uses Akismet to reduce spam. Learn how your comment data is processed.