The idea behind this series is wonderful; unfortunately, the execution fails miserably. The revised version while tremendously better than the original is still a complete waste of money. The depth is about right for a 1st - 3rd grade level. The experiments, and that term is used very loosely with these books are usually cheesy, even to kids. The work that it would take to adapt these books to use for a child above the 3rd grade would be tremendous and the end result would be that you maybe used the table of contents as an outline. Even though the depth is appropriate for around the 1st - 3rd grade level the interest and fun really isnt there. While these books are written from a Christian perspective even that isnt done as well as it could or should be. Please dont waste your money these. For children in 4th - 8th grade there is a wonderful series that includes Exploring the World of Physics, Exploring the World of Biology, and others. These are wonderful, interesting, factual, Christian science books. Bob Jones and Apologetics are also excellent choices for all grade levels.