I can't seem to wrap my mind around this scenario... a pond in a classroom? Or is it just outside the classroom?

If inside, how big is it, how deep, what sort of bottom soil does it have, and (most importantly) how much light does it recieve? Is it supposed to be functional or [like the mural] representational?

It sounds like a classroom assignment to me. Send the kids to google up what you want.

It sounds like you want some fairly tough low-light tollerant easy going plants, that won't run an arm and a leg. Annuals indoors will tend to get leggy in low light, but if the ones you grow will root easily, you could just take cuttings whenever the planting looks bedraggled. Could make that into a class project, too.
So I'm thinking maybe impatiens, geraniums, and coleus would all be good candidates as they should root well from cuttings.

pansies, petunias,

You can google indoor water gardens and get some ideas. I would stick to native bog/marginal plants like pitcher plants, ferns, cattails, Louisiana irises (or other types), maybe native violets, rather than African. You can also have a few water lilies in there. Good luck! It sounds like a fun project and a progressive school! A few "tropical" plants wouldn't look too bad, I wouldn't think. Like some papyrus, cannas, elephant ears or philodendrons. Just for filler in the back part. You need some height. You could also put some bamboos or sedge in some pots.

HW

Here is a link that might be useful: here's a schoolyard pond for indoor or outdoor