This post comes off the back of a CPD session that a colleague of mine ran for us. His CPD sessions this year have been among the best CPD sessions I've been to because they're all very practical. This session in particular was about checking for understanding - the importance of doing your CFU in a way that gives you good data. Are your student responses reliable? If a student gets the question correct, is it because they knew the answer, or did you give them a 50:50 choice and they had a lucky guess? He went on to talk about the importance of stretch it* and sort of excavating the reasoning behind an answer to further increase the reliability of your data.
I came up against this, specifically the latter point, in a lesson today.
Picture the scene. Bottom set year 8, after break. Elements, compounds, mixtures.
They're a group with very low recall and appalling memory. They make goldfish look like elephants, bless them. So I take it nice and slow. Explain what an element is. Give some examples in the form of diagrams. Define an element. Give a few non-examples. Pause for CFU. Mini whiteboards out. Means of participation given clearly. We are ready to check that understanding. Now at this point, the only questions I can really ask to check if they've got it are "what is an element?" and "is this an element?" which doesn't really check understanding. The former is just regurgitating what I told them three minutes previously, and the latter is one of those useless 50:50 questions. So I add a second part to my question - "why?"
I draw this diagram and I ask "is this an element: yes or no? and why". The why lets me into the students' heads just a little bit. I can begin to excavate their thinking. So this student, I'll call him Liam, writes on his mini whiteboard "yes because they're all green". Now that's not really correct. I'm looking for "they're all the same type of atom" but this student really struggles to articulate himself, so I'm thinking "maybe he gets it, he's just bad at wording it". With another group I'd interrogate his answer - "what do you mean 'they're all green'?" - but I know this student takes a long time to collect his thoughts, and I know that with this class, if I did that and gave him enough time to explain himself the ratio will completely drop (if I'm lucky) and if I'm unlucky they'll start like rioting or something. So I have to try a different tack. I know I could ask one of the other students "what is wrong with Liam's answer?" but I also know that Liam probably won't respond well to negative feedback from his peers. Instead, I tailor my questions for him a bit more than I would perhaps do normally, and I resolve to check his board first on the next one:
So I go for a third question and I'm pretty sure I know what his answer is going to be.
If you guessed "yes because they're all yellow" give yourself a mark.
He didn't get it and I needed to go back over some stuff with him. [Turns out he'd forgotten the bit where we said we represent atoms as circles and thought that size didn't matter. Thankfully most of year 8 are still innocent enough that I could say "size always matters" without them rolling up laughing.] But if I hadn't asked "why?" I wouldn't have known this. I would have no idea how he'd gone from having it right to, seemingly suddenly being wrong. I'd be there asking "what happened? Why did you get that one wrong? Were you not paying attention?" By asking "why?" I can get that insight into his thinking, what is it that is actually going on in his head.
I think that the "why?" is a very useful question to have in your in your repertoire, in your bank of things, because "why?" helps you to know what's going on in the kids head, but it's also quite useful for if a kid gets a question right to push the student further. Justifying your answer takes a bit more than just guessing. Obviously, there are some things where it doesn't work so well - "what are the forces of attraction like in a solid?" "ok why?" G-d knows, especially not year 7 - but a lot of the time it's a quick and easy way to 1) check they actually get it, and 2) push them further
TL;DR
"Why?" is useful as part of a CFU and to stretch it.
*Technique from TLAC where correct answers are "rewarded" with trickier questions