you could........get a bigger tank!!! I have a 55 gallon african cichlid tank in my classroom, it is AWESOME!!! The kids LOVE it and help take care of it (help with water changes, they measure out the food for each day, they use the MagFloat to clean the glass, help with rock placement, etc..).
With a 1 gallon bowl, you are doing to have difficulty keeping much of anything, IMO (does it have any type of filtration or oxygenation?). I would be worried about weekends (especially the 4 day variety) if you don't have any type of filtration (especially if you go with more than one fish....possible ammonia issues). You will also have to do frequent water changes (assuming that you don't have any filtration....which is an assumption). If your principal allows it (and you want to do it), I would look on craigs list for a nice used set-up in your area, or you could put something in a newsletter asking anyone if they have an aquarium that they don't use anymore, we actually had a grandparent donate a 40 gallon aquarium with all the fix-ins (filter, stand, hood, light, pumps, siphon hose, etc...) this year...all they wanted was a donation slip.
What grade do you teach?