As a southern hemisphere school we have just had our mock exams, so I thought about way to return them for the biggest impact. I put the question to twitter and got some great responses (given that it was the summer holiday for UK teachers).
At lunch today, a colleague and I were talking about Trig, and one thing that came up in conversation was that if a+b=90 then sin(a)=cos(b). Not that this was something that we did not know, but it certainly was a case of the curse of knowledge as neither of us could think of a time we actually taught this to our students. We both felt this was a useful thing to explicitly teach them.
I had a good lesson (as far as it can be judged at the time) with my IB Higher Level class this week where we started implicit differentiation.
With my 6B IB Maths Studies class we are revising for the final exams, and we were looking at quadratic functions, a topic they particularly struggle with. I got them to work in pairs to write up all they could remember from the topic on a whiteboard.