My daughter is eight and just loves this series. She recently requested that I borrow the Mammoth Hunter one from the library again, so I just went ahead and bought it from Amazon. It is funny, the information on the book says that the reading level is for ages 4-8. No wonder the 1st Grade teacher was confused! This series is marvelous for 3rd - 5th grades, as the other reviewer said. They are rather sophisticated in layout (many fast-paced "blurbs" of informtaion splattered on the pages instead of a slow, steady narrative), language, and themes. But, how fun is it to learn the down and dirty aspects about historical times and cultures? So fun! Really a hoot of a series. Not only does my daughter thoroughly enjoy these books, but I've purchased them for my friend's son who is a couple years older, and he loves them, too! In other words, I think that these books will have a long shelf life in the interest realm of your child.