Textbooks on evolution
Futuyma, Douglas. 2005. Evolution
Futuyma, Douglas. 1998. Evolutionary Biology, Third Edition.
Ridley, Mark. 2004. Evolution, Third Edition.
Freeman and Herron. 2004. Evolutionary Analysis, Third Edition.
Each of these has its strengths and weaknesses, and I only got Futuyma's latest about two weeks ago, so I don't have an opinion on it yet. All of these are available in the library, so I suggest you look through each on a set of topics and use the one that you find most helpful. There are some other textbooks out there, but they tend to be more suitable for non-biology majors, so I don't know them well. It may be that they would be good for middle school and high school students.