~Viva~Per~Amore~
I would say give them a pie, since that is what my math teacher would give us on pi day. Yes there is such thing as a pi day.
That is actually a Really Really good idea
or maybe you could funky up a calculator, like get one of those giant ones then pull it appart then put it back together all color awesome
pin boards are functional and easy to decorate, paint the edges then glue some pretty paper over the top, but not more than one or two layers of paper or the pins won't go through easially
or you could make plush anything math related with felt
am I any help?