Two Plus Two Is Not Five by Susan Greenwald, has been instrumental in helping my children visualize math concepts. It turns a bunch of numbers on paper into something real and tangible for my children to work with. As I was teaching them some of the math tricks in this book, I realized Susan (the author) had found a simple way to explain exactly how I actually see math problems in my mind. I never could have explained it this well. This curriculum is easy enough for my 5-year-old – he loves it and asks for more – and yet is still interesting enough to help my 9-year-old fill in some gaps in her math knowledge without being bored. I highly recommend this curriculum.