What are cusinaire rods?

Answer 1

these are a series of colored wooden "rods" - really, blocks - used to teach basic number theory and math skills. They were invented by Georges Cusinaire, a Belgian math and music teacher, in the 1950s. There are ten different "rods", all of which are the same height and width but they differ in length. Each one is one "unit" longer than the previous one, and each has a different color.