I'm Doing Volunteering at a primary school.
One of the things that we're keen on is teaching mathematics via games.
I'm looking for games that people have found are good for this (either designed to teach, or as a side effect).
EDIT: These kids are generally at the stage of learning adding, subtraction, multiplication and division.
EDIT: I should have made it clearer that as this is school volunteering at a (for want of a better word) deprived school, something that requires computer access is not appropriate. Board games would be fine, because I can bring them in.