[Session: Eugenia Etkina – Pedagogical Content Knowledge (PCK)]
What you believe about how people learn, and about the role of teachers and students is in the classroom, WILL affect your teaching.
For example, do you believe that a student misconception is something that needs to be eradicated with a clear example that clears up the misunderstanding? Or do you think that the misconception will always be there? What you believe will affect how you teach.
Take for example the idea that horizontal and vertical motion are independent.
Here’s one way to teach this.
Predict and explain
Show students an apparatus that can drop a ball down and shoot another horizontally. Ask your student
s to predict what will happen if a ball is shot horizontally and dropped straight down. Most (if they haven’t seen this befre) will predict that the one dropped straight down will hit the ground first. Show them the experiment, or a video, of a ball that drops vertically and one that is thrown horizontally. They will, in fact, hit the ground at the same time. But you’ll find that students will debate this. Because they have a certain expectation, this actually affects their perception – they literally hear the balls hitting at different times. You can slow down the video and see that they do hit at different times. But, studies have shown, they’ll find ways to rationalize this, like “air resistance” so that what they see stil fits within their understanding. The misconception is really robust.
So, here’s another way to teach this.
Observe and explain — then predict
Show a video of a cart that is moving horizontally. It throws a ball up which rises in an arc and falls back into the cart. What do they see? It falls back in the cart. There’s no arguing against that. Some students will think that there must be a magnet bringing the ball back (though you can show that it’s a wooden ball). Others will notice that the ball continues moving horizontally while it’s moving up and down – it’s keeping pace with the cart. Great! That’s what we want them to notice. You can then show them a woman on roller skates, throwing a basketball straight up. She catches the basketball and it’s easier to see that there’s no magnetism involved, and you can see the mechanism
of the throwing (her hands move straight up). Great, so now we have the idea that horizontal and vertical motion are independent. NOW go to the first video, where the ball drops and is thrown horizontally. Ask them to use the idea they just learned to predict what will happen! Not their intuition. As scientists, we use ideas to predict, not intuition. If they use the new idea – that horizontal and vertical motion is independent – they’ll give the correct prediction (that they will hit the ground simultaneously. Their job now is to figure out why their intuition brought them to the wrong place. There is something in that idea that is useful, just not in this situation (some might call it a phenomenological primitive, or p-prim).
But it’s best to address that misconception after the new idea has been created. If you show them the experiment that flies in the face of that misconception – first – they may not see or believe what it is that you want them to. This sort of full-frontal “force students to abandon their wrong ideas” isn’t effective. The almost sneaker, back-door kind of approach to show them first what is, create a new idea, and then apply that idea to a situation which they may have naively predicted the wrong behavior, seems to be more effective.