In many traditional classes, students are shown a demonstration either during, before, or after the teacher explains what is to be demonstrated. The idea is that seeing and hearing is believing, and that it’s better than just hearing. I think it’s also implied here that actual “real-world” examples (ones you can see and touch) help students relate to the concepts and that demonstrations get students paying attention better.
In many reform-oriented classes, students discuss predictions before observing the demonstration, and only then the teacher explains. The idea here might be that asking for predictions helps students commit to an answer, perhaps causing some cognitive conflict when they observe something discrepant, and that now they are ready to hear the explanation. There’s also the idea that students might hear alternative explanations during discussion, some of which will be close to the right explanation.
In fewer reform-oriented classes, students go back and discuss the observation; and only then after having discussed it again, the teacher uses the ideas that arise during discussion as the basis for explaining. The ideas here are (1) students need time to process what they’ve observed and to begin to put some of the pieces together before they hear an explanation from the instructor and (2) discussion allows a teacher to tailor the explanation in a way that helps students make connections between their ideas and the explanation.
In far fewer reform-oriented, students will then have to make a new predictions about some new situation in light of the new ideas that have been discussed and explained. The idea here is that the understanding can be fleeting and that knowledge can be very context-bound. By letting students try to apply the same idea to a new situation, some nuances will arise about what it actually means to understand that concept or what it means to be able to apply that knowledge in a new context. The teacher also gets some additional evidence about how well the students understand the concept, in terms of its “span” not just “depth”.
We did all of this in my class, except that I never gave my explanation. I only tried to help us all better understand all the explanations we’d heard. Lots of ideas came up about “Why we didn’t see a beam in the hallway”. Instead of me telling them what situation they are supposed to make a prediction for, students came up with the new observations they’d like to make. They each made their own predictions and explanations for why we would or wouldn’t see a beam of light. Now, they are being sent home with express purpose of making those observations and reporting back to class.