As I was reading Invent to Learn, I was reminded of the tray of Cuisenaire Rods that inhabited the coffee table of my childhood. My sisters and I built things with them and played with them. I guess we learned about relationships between the rods and all of the other inherent properties, but since that time, I have run across quite a few nice resources that use C Rods to help develop basic math concepts. The ones I ordered arrived today. Now to find time to work those into the time I spend with my children.