Game Theory: A Non-Technical Introduction to the Analysis of Strategy
This is a very easy to read book, full of great figures, explains from a somewhat more Economic perspective than a Mathematical one, but very cross-disciplinary like the subject itself. Sounds like it would be worth looking into for high school students.
Full Disclosure: I took a class with the writer of the book, so his teaching style may have utilized it more fully than others. That class was listed as in the Economics department.