All good for 3rd or 4th grades. Maybe a bit younger for some. I bought a lot of books my students and daughter grew into.
1. $10: math books for elementary school aged kids who enjoy math and 2 science project books. The brain teaser book is unused...lots of cool brain teaser puzzles to fill in.
2. $10: Two ocean themed books--I esp like the under the water book. The other lift the flap one is good.
3. $10: Engineering books and book on flying machines and one on how things work. I really liked those last two. The engineering book and challenges one are good too. The challenges one has more wear--included for free.