For my own child I have accordian folder with dividers for each year.
Well, really, wouldn't you know, he found something with his name on it and it disappeared again! Humph
Before I go track it down... again, I'm going to rely on memory (the other years are in storage right now). One section is for IEP's, one for evaluations's, one for correspondence, and one for misc. information. This really helps me to stay organized and to be able to quickly compare years if I need to. i.e. I can get grade 9 out to compare to grade 10 to accurately determine goal advancement, what worked or didn't work, and help decide if additional data is needed. I also know exactly where to look if I need to pull out an emai that I sent or was sent to me regarding my son.