Contest math, Grades 4, 5, and 6, MathLeague, (unused/new): $8
Logic Problems, 110 puzzle problems, great for stimulating logical thinking in elementary and middle school children (unused/new): $5
The Everything Kids' Science Experiment Book, Tom Robinson, (unused/new): $5
https://www.simonandschuster.com/books/The-Everything-Kids-Science-Experiments-Book/Tom-Robinson/Everything-Kids/9781580625579