Chinchillas are cool, but I would think that temp. in Miami might be an issue for them (they are also messy ~ little pellets everywhere, easy enough to clean up), but they are a rodent, and they eat and poop 24/7. Chins are also usually pretty expensive. Snakes I would stay away from (esp. with 3rd graders), in my experience they get out way too easy and way too often. Turtles I would stay away from, most of the water dwelling ones carry salmonella and their cages will reak unless they are cleaned daily (definitely not low maintence), and most species of box turtles are no longer legal to possess.
Bearded Dragon as Z said would be good, or if you want low maintainence and nonhandable, consider green or brown Anoele (sp) or baskalisk (sp) lizards (definitely low maintainence, not smelly or noisy, but fun to watch ~ they do not however like to be handled). Hermit crabs are also always fun, as are salamanders (although most of them also carry salmonella). Hedgehogs also are not too bad, and I know another teacher who kept a bunny as a class pet (it chewed a lot of things ~ including power cords, but wasn't too bad). I've never tried a bird, so I know nothing about them.
