I have to find an interesting activity for some 11-year-olds moving to high school this year. It is supposed to take about 30-45 minutes, and I thought of having a mathematical theme. I can make a large tangram, and do that. Pentominoes have some interesting puzzles attached. I could make a large Soma Cube - or get someone else to do it, but cubes of the right size to stick together seem hard to come by. There are some neat dissection puzzles, too. It would be possible to have several challenges done in rotation.
We're outside, and groups of up to 20, so there could be a competitive element. I want the thing big enough that if I split them into two or three subgroups they can all get involved.
The main thing is to have fun, but it would be great to get beyond that in a mathematical direction ...
All contributions welcome.