There was a really good video I once saw on Teachers' TV ages ago where a teacher was doing a science lesson (on light IIRC) and using the kids as experts to help each other. She also used the traffic lights for AfL in her plenary. I thought it was a really good lesson and there was something in it that I really want to try out now with my class. Problem is, I just can't find the video. No idea what to use as a keyword search either. Does anyone know which video I mean and, if so, do you have a link to it or anything that might help? Thanks in advance.