I have one folder for each class in which I put their finished flat pieces and photos of 3D things. I keep the folders in a big box that accomodates 12x18 paper.
Just before the end of the trimester they each make a construction paper (18x24 folded in half with one end turned up) portfolio. I pass out all the artwork and they put it in their portfolios to take home.
In Nov. we have PT Conferences, and they take them home then. Conferences for me are optional and pretty much drop-in, but most of the portfolios end up going home. The rest go home the next class day.
It took me 3 years to work out this system. I'm down to about 500 students.
Susan in OR