Houston ISD said it was aware of the issue and was monitoring temperature readings.
"Our campus is currently experiencing ongoing issues with the air conditioning system. The District's HVAC team is actively working to resolve the problem as quickly as possible," the school principal said in a note to parents.
School officials added that students were temporarily relocated to cooler areas on campus while waiting for spot coolers to arrive.
The ongoing problems led the district to close the school early, and transportation was being arranged for early dismissal.
Parents are asked to pick up their kids as soon as they can.
"For families unable to make immediate arrangements, please rest assured that we are taking every possible measure to keep students safe and comfortable until they can be picked up," the letter continued. "Thank you for your understanding and cooperation."