I like "The Quantum Universe" by Tony Hey and Patrick Walters. The math is specifically aimed at high-school level and it is full of pictures. It really gives a feel for what doing quantum experiments is like and gives lots of applications. Of course, Schroedinger's cat et. al. also make an appearance, but the book is more about the successes of the theory than about it's conceptual difficulties. Every high school should have this book in their library in my opinion.
I also like "The Meaning of Quantum Theory" by Jim Baggott. It is aimed at explaining the conceptual problems of quantum theory to chemistry and physics undergrads. It has more math than a popular science book, and you may need a little calculus and linear algebra to follow some chapters. However, it's not as much as in a standard quantum physics textbook, so if your student is strong then they might enjoy the challenge.