I just started reading this set together with my 3-yo son. He is fond of the main characters in this series, Sally, Seth, and Tanner. But overall I think the stories are not very engaging or challenging. He's already exposed to the main concepts, like shapes, sizes, simple sequences, sorting and matching, from many other sources. Maybe we or his school had over-prepared him for reading but I feel that this series is not challenging enough for him and we could have probably skipped this series and gone right onto the beginning readers set. Oh, did I mention that these books are really pricey? I admit that I got them on a sale but I would probably not want to pay retail price for them.