LEGO is great for teaching kids math concepts. I've used stacks of Duplo bricks to practice addition - i.e. 'put the stack of two bricks together with the stack of three bricks, and how tall is the tower?' And I've previously noted helping my daughter learn her 2x multiplication table. Here Erin from the So you call yourself a homeschooler blog is using stacks of bricks to teach fractions.