This far into our homeschooling adventure I have found that math is our most costly area of learning. There are many Montessori materials that are used to teach the concrete concepts before moving into abstraction in Montessori. I find this process both fascinating and highly effective. For example I taught my son addition and subtraction using math beads and after exploring the material on his own for some time he discovered the idea of multiplication on his own. The materials are so hands on that children get to experience that joy of discovery even in ideas that would typically be thought of as too abstract for young children! That all being said there are still plenty of money and time saving tricks and DIYs in this area as well, but there are some materials here that are really worth the investment!