Unfortunately I can't be of any help in recommending any particular plants, but I gotta say you are one great person for doing a project like that for the kids. I wish some of my elementary teachs were like that, heck even some of the High School teaches I have now. I hope your pupils appreciate what a teacher they have in you!
~Jordan Land

You ARE an awesome teacher! I would have LOVED to do that in school! I don't know what kinds of plants are generally sold in flats, but it sounds like perhaps the kids are overwatering their terrariums. (Just a guess). Ivy and moss should do very well. I haven't heard of needlepoint ivy, but I assume you mean english ivy. Ferns are also perfect, and since they are sold so cheaply in little 3" pots, I would imagine they would be sold cheaply in flats. African violets probably rotted because the soil stayed constantly moist. Check out the thread below for some more great suggestions. I have found that fittonia does very well indeed, though the leaves may be a *little* large if the terrariums are very small. Good luck!

Here is a link that might be useful: Plants for Closed Terrariums

Congrats also for doing this for the kids. With 120, you should check if you can wholesale order some ferns, Selaginella, or similar online. The ferns should be readily obtainable, as they are mass tissue cultured and then sold to growers as small plants in cells. An online search should located a wholesaler, which should be cheaper for you. Better yet, maybe a local greenhouse place could actually order them for you, if they are ordering for themselves at the same time you may save on shipping. Carnivorous Plants may also be good, you can grow them on straight peat moss or a mixture of peatmoss and sand (not regular potting soil, and NO fertilizer). They love the humidity, and the kids love that they are carnivorous (they also grow faster and easier then flytraps). Two common and good tropical sundew species are Droser capensis or Drosera adelae. You can also get seeds of these, they must be sown on the surface of the moist peat. They are slow at first so may not be the best bet for kids. Biological Supply Houses (i.e. Carolina) may also have flasks of tissue cultured sundews ready to be separated and planted (may be more expensive this way). If interested in seed, check out the INternational Carnivorous Plant Society, I think they have seeds of some common types availalbe to schools, but not sure.

bamboo?

Thanks for your suggestions and kind words. I really don't deserve any special praise...just doing my job like lots of other people do. And the kids are fun.

IME, African voilets, & fittonia do very well in a highly humid enviroment.