Separate presidential libraries are a generally a 20th century phenomenon–previously presidential papers were usually kept by the National Archives or in historical societies.  The privately funded museum/library/shrine of modern presidents has many advantages, and some drawbacks.  The advantages are that there is a focused, dedicated staff collecting and arranging material, and the drawbacks are that each library has its own way of listing material, so that there is no consistency.  However, these libraries contain a great deal of information about the period, not just about the president.   Many of the libraries collect oral histories of people associated with the president, and many have copies of archival documents, which can be easier to plow through than the nara.gov site.   All of the libraries are listed at

http://www.archives.gov/presidential-libraries/contact/libraries.html

though of course Google will find them as well.

It is a good idea to look for a Research button on the home page–many of the libraries stress material for high school students.   But perhaps someone would really like

Hoover Wore Many Hats, an interactive game for children of all ages. Play the game!