"It's bad enough that when you enter the class, sometimes you see them drooping. It's bad enough that you wonder as a parent how they are able to learn," said Regina Leibman who has a ninth grader at the school.
School leaders say an electrical surge at a nearby power station caused the problem. It cut electricity to part of the school and shut down portions of its air conditioning system.
But, parents complain problems with the cooling and heating system occur year-round and Principal Tom Hatch said he is aware.
"Our HVAC guys have been working hard this year to keep all the units up and running and continue to do that each day," he said.
School officials said they considered cancelling classes.
"At one point, we thought that we were going to have to an early release," said school spokesperson Theresa Perry.
But it never came to that. School officials said the entire cooling system was back online by late afternoon.