I have a 4 drawer file cabinet. I keep everything by child and by year. It's not required because we use a charter school but I want to just in case. Once the cabinet is full, I will throw out the oldest year. So far it is 4 yes and I have filled about 2 drawers.
I am trying to figure out what to start keeping next year. We will be going on our own next year. This year we are using k12 and it is not a big deal to throw almost everything away. Though I do keep most of the really cool art work that they make if I am really impressed.
What I do is keep the work that needs to be worked in seperate drawers and the ones that are already worked in, I keep a few good ones and a few not so good ones for posterity's sake, in another drawer. Then I keep everything else in a box like we are moving and if I need to I can just throw them away. :)