When Students Learn (or don't learn) from Classroom Demonstrations by Bill Cerbin

Classroom demonstrations are used widely in college courses to help make abstract ideas more concrete. For example, MIT Physics Professor Walter Lewin (below) demonstrates the period of a pendulum by suspending himself from a long cable attached to the ceiling of a lecture hall and swinging back and forth in front of the class. The demonstration is intended to attract students’ attention and engage them in thinking about the concept he just explained.

 

But research indicates that students who observe standard demonstrations in class perform no better on related test items than students who do not observe the demonstrations. This finding led Harvard Physics Professor Eric Mazur and his colleagues to consider alternative ways to do classroom demonstrations. They discovered a simple and potent method to improve student learning from demonstrations. It goes like this:

1. First describe the demonstration to students and ask them to predict the outcome of the demonstration. The Mazur group asked students to select a prediction from among several options (multiple choice) or to produce their own prediction (open ended).
2. After they predict the outcome, show students the actual demonstration.

The addition of the extra step—predicting the outcome—improved student learning markedly on test items related to the demonstrated concept. The researchers also found that for particularly difficult concepts, demonstrations were most effective if students predicted the outcome of the demonstration and then spent a few minutes explaining their reasoning in writing or verbally to classmates before observing the actual demonstration.

Why should predicting and explaining improve student learning from demonstrations? Maybe you would like to stop at this point and formulate your own explanation before reading on . . . but here’s what is happening.

 

In a standard demonstration students observe the instructor carry out the procedure. Like the wild physicist swinging across the room, it may capture their attention but they are left to their own devices to make sense of how the demonstration maps onto the concept. The connections between the concept and the demonstration, obvious to the instructor, may be invisible to the novice. There is nothing in the event itself that engages students in discerning connections between the abstract concept and the demonstration.

 

In an enhanced demonstration, predicting and explaining are sense-making activities in which students try to discern the connections between the concept and the demonstration. They construct a model of how the concept works. Their models may be half baked or seriously flawed but represent an emerging understanding of the concepts. Subsequently, when students observe the actual demonstration the outcome is feedback that will confirm or contradict their understanding. If students were thinking aloud at this point we might hear them say things like,

• “Oh, I was on the right track; my prediction is correct. I get it.”
• “Oh, I was sorta on the right track but it’s somewhat different than I thought. Now, I understand it better.”
• “Oh, I was dead wrong, way off track. I was thinking that it was X but it’s not; it’s Y. 

Broader implications for teaching. Teachers use demonstrations, examples and diagrams to illustrate and bring home complex concepts and principles. The design of the demonstration or example is important but what matters more is what is going on inside students’ heads during instruction. The demonstration does not make the concept self evident. Students have to work out their own understanding. As teachers we can influence the way that students think about concepts by asking them to predict, explain, summarize, analyze, evaluate, speculate, interpret, critique, decide and so forth.

 

References

Crouch, C.H., Fagen, A.P., Callan, J.P., & Mazur, E. (2004). Classroom demonstrations: Learning tools or entertainment? American Journal of Physics, 72 (6), 835-838.

 

 

 

This work by Bill Cerbin is licensed under a Creative Commons Attribution-Noncommercial-Share Alike 3.0 United States License.

Comments

[Tim Tucker]

Students do pay attention to what you teach them. Some times as teachers we think they don't pay attention but they do. The students love to see a teacher make mistakes , so sometimes I make one on purpose to keep them involved. Most of my class is hands on, so when I see a student making a mistake I go ahead and let him, for we all know as teachers that is when we learn. You do not make a mistake if you learn from it.