I get a lot of inquiries regarding books on economics that might be suitable for younger readers, say between sixth and ninth grade. The three titles I recommend are:
(1) Lessons for the Young Economist by Robert P. Murphy. You can read this book for free online, but your student will want a hardcopy. It’s a very attractive, large-size textbook on good-quality paper. Thorough in scope but basic and understandable in exposition.
(2) How an Economy Grows and Why It Crashes by Peter D. Schiff (with Andrew J. Schiff). A very accessible book for young people, complete with illustrations and characterized throughout by the clear exposition for which Peter Schiff is well known.
(3) Whatever Happened to Penny Candy? by Richard J. Maybury.