If you’re looking to build up your home library or to review books before you buy, or if you want to print the classics yourself (perhaps in a large double-spaced font for note-taking and easy focusing) then you’ll want to check out these links:
Free Books Online; Classics
Classics Online

And here are reading lists to help determine which books are appropriate for which age groups

The NEH has divided their list from kindergarten through high school. The College-bound reading list is specifically for high schoolers headed for college. The Kids Reads list begins at birth and goes through high school, too.