Review of Mathematics Galore: The First Five Years of the St. Marks' Institute of Mathematics by James Tanton

The author has gotten high school students into mathematics research via workshops and a newsletter that had expository math articles in it. This book is a collection of 26 of those newsletters. There are also several appendices some of which have original research done by the students. Even though a high school student can understand the material it is interesting and sometimes surprisingly difficult. The chapters are well written and motivated.