It is very, very important that an adult set up the light for the pond in a manner so that it can never fall into the water. Water and electricity don't mix. Anything that involves a plug needs adult supervision. Goldfish, tadpoles and snails are hardy critters to keep in a classroom pond. The anacharis helps keep the water clean and supplies oxygen to the fish.
Marginal plants do well with a couple of inches of water over their crowns.
Jobe Plant sticks will keep them growing. Cover their soil with aquarium gravel to keep the dirt out of the pond. Spider Lily A filter should be set up in your pond. That cleans the water and keeps the fish healthy. There are all sorts of inexpensive filters available at the pet store and an employee can help you find the kind that would work in your pond.