Insulating your classroom trout tank is absolutely crucial. It keeps the water at a more constant temperature, which saves wear and tear on your chiller and also keeps the trout much happier.
Because it is important for your students to see the trout as the develop, it is acceptable to leave the front insulation off of the tank, as long as all the other sides (and bottom and top) are covered. However, only do this AFTER the fry have absorbed their yolk sacs and have started feeding. It is only then that they can handle the light for long periods of time.