Use movement or a tableau to "show me a concept".

This often works best with groups further down the years, but occasionally a group of 6th formers will get into it.  The basic idea is that the students are put in groups and given a concept (or sometimes concepts) to represent.  They're only allowed to use their bodies, no probs, no signs and, most importantly, no talking, to illustrate the concept.  They have to illustrate it using up to 45 seconds of movement and ending with a strong "still" picture.

When using concepts that are new to the students then scaffolding materials, texts, pictures have to be used to help the students access the concept, otherwise this is an excellent way of revising or looking at topics from another angle.