What a wonderful idea that you can continue to use as your child progresses to school. As a smart person commented, as your child reaches high school, they could be holding a chalk board with the grade written on it. I always had the kids signify their grade by holding up their fingers. But the pained look on their faces by high school discouraged me not to insist on that little detail.
A box for each kid K-12 ... I had a professional organizer at my house (what a treat!) and she suggested this system for pictures and papers, etc. 1st year, 1-2, 2-3, 3-4, pre-K, K, 1st grade - 12th. So simple, but so brillant.
With her first day of pre k quickly approaching I am desperate to find cute ideas for first day pictures, I like this one a lot, and it could be a lot of fun if I take it in front of the mural by her class room, make it more memorable :)