Some years ago, we stumbled upon these books at the library. They were an instant hit - every single one in the Sir Cumference series! We check out lots of books but this one the children remembered. In fact, we hadn't checked these out for a couple of years when one son started a new geometry section in math and asked me to get these again so he could review! My preschooler thinks of these as fun stories and enjoys the illustrations while the older crew is making the connections to mathematical concepts they are learning. For example, one child always keeps diameter and radius straight because of the book characters (Radius is the little guy!). I highly recommend this series as enjoyable literature that will help your children remember their geometry. The books also have an object or character (jester, seagull, rat, cat, etc.) that appears on most pages which is an extra bit of fun to look for. I love the rich colors and oil painting technique too (I may be wrong about the oil painting but that's the feel of it). I decided these belong in our home library and was especially pleased that Amazon was running its buy 3 get 1 free promotion just then.