Gather all your children's school papers, and separate them into piles. Each child should have her own pile for each year of school. If you organize the school papers at the end of each school year, you'll find it easier to maintain order.
Go through the papers one school year at a time. Separate the papers into "keep" and "discard" piles, using the two boxes or bins. Keep the papers, artwork, essays, report cards or other special assignments that reflect the best of your child for that year. You may want to keep some of the bad assignments as well to show his growth. Throw away reminders about holiday closures or routine assignments. Sort papers by subject, or put the papers in chronological order if you want.
Determine the best filing system for you. Keep each child's work in her own folder, bin, file box or other storage container, and file her work by year. For example, a folder can have protective sleeves to preserve her work and use tabs to separate the assignments by year. A plastic filing crate can have hanging files, or you can stack her work in a plastic container or basket with papers separating her schoolwork by grade.
Take pictures of your child with his projects or large assignments that are too big or bulky to store. This allows you to preserve the memory of the assignment without having to rent a storage unit to save your child's schoolwork. Include the picture with other pages from that school year.