I came across Wilbooks today and they have a cool little program for getting books into K-2 classrooms. The site points out the fact that there are many schools without the supplies and books necessary to help students succeed—even the fact that many teachers spend their own money to buy classroom supplies and books doesn't completely fill the gap.
The program, "Back to Basics," assists students and teachers by collecting and distributing classroom supplies and new and gently used books.
If you'd like to donate supplies or new or gently used books at any reading level this page provides information on their needs.
If you'd like to apply to receive supplies or books, you can find that information here.
The Back to Basics program is just one of the many programs that Wilbooks runs; they also sell all their books for just a few dollars each.
As a side note, their summer reading program currently has a great deal for getting books into schools—for every book that a school purchases at the regular price (an extremely low $2.00 a book), they will donate a book to the school.