At a local Math Circle, I loved some problems worked out through a hinged mirror to illustrate symmetry. I bought a hinged mirror from hand2mind.com, and am looking for some material, ideally books about symmetry that encourage use of the mirror, but .pdf diagrams as well. Does anybody have any pointers? Thanks.
It depends what level you want. There are mirror activities for young kids in Moebius Noodles (by my publisher).
You could do platonic solids via their reflection groups. There is some material here: http://www.cutoutfoldup.com/818-platonic-solids-kaleidoscope.php
There's also Conway et. al.'s The Symmetries of Things which has some mirror related material in the beginning. However, I think that would be something to build material out of rather than use directly.
I understand that this is an English-language based platform but I thought it could be of some interest to share with you some links to projects about symmetry in Italian primary schools. After all math is an universal language, isn't it? Well, well,... at least I hope that pictures are self-explanatory.
On a personal level let me add that I personally tried, with some fun, having kids explore symmetries in Escher tessellations Escher