Well, it seems that the Prang watercolors are the way to go!
I really like the idea of having the students have their own box to take
care of. I think it's important to give them ownership of as much as
possible. With over 450 students, however, I'd have to come up with a
sure-fire storage system for each class. Also, with only one small sink in
my art room, clean-up can be difficult. I usually have one or two students
volunteer to do the sink work. But if the students work neatly from the
start that shouldn't be an issue with watercolors.