How hot is it in classrooms without air conditioning? BPS data can tell us.

Second-grade teacher Kevin Moy brought his own fan to his classroom at the Mather Elementary School in Dorchester.David L. Ryan/Globe Staff

It’s the first day of school for Boston Public Schools students, but it sure doesn’t feel like fall.

Temperatures in the Boston area Thursday were forecast to soar into the 90s, prompting some districts around Massachusetts to cancel school or send students home early due to lack of air conditioning in school buildings. But how hot is it inside classrooms, really?

BPS last year launched an indoor air quality monitoring system in classrooms across the city that collects real-time data about temperature, humidity, particle pollution, and more. On hot days like Thursday, the data ― which are publicly available in the form of a dashboard ― show temperatures and humidity levels inside classrooms without air conditioning.

The vast majority of BPS schools are air conditioned, according to city officials. But there are 13 among the district’s 134 school buildings without A/C. Among those schools, 11 had an average room temperature of above 80 degrees as of 11 a.m. At one school, Mel King Prep, the average temperature reading was 86.7 degrees. Two rooms at that school showed room temperatures breaking into the 90s.

It’s a stark contrast to the situation in air conditioned schools, where data showed temperatures in the low 70s as of Thursday morning.

Bridget Galvin is a fifth-grade inclusion teacher at the Haley Pilot School in Roslindale — one of the campuses where BPS had not yet installed air conditioners as of the start of school.

”It’s just really hard to keep the kids on task,” said Galvin. She’s been bending certain rules, she said, like letting them put their heads on their desk when needed and taking more breaks than usual. A friend of hers dropped off a case of water for the kids, which she said was a life-saver.

”It’s just oppressive,” she said of the heat. Galvin’s classroom doesn’t have any windows, and she is relying on two fans to stay cool. The temperature has been around 82 degrees — higher when the 72 percent humidity is factored in.

”We’re just getting a lot less done than usual,” Galvin said.

To be sure, the temperature readings represent just a single snapshot in time on a hot day, and don’t necessarily represent typical conditions. But BPS leaders said they use the temperature data to make decisions about when to close schools.

Superintendent Mary Skipper said during a morning press conference on Thursday that school officials were responding to the heat. School leaders made sure there were ample fans in the schools that don’t have air conditioning, she said. They also opened windows early in the morning to get cool air in, and planned to do so at night.

In a statement, BPS spokesperson Max Baker pointed to improvements in air conditioning facilities at schools around the city.

“BPS students must have healthy and safe learning environments,” Baker said. “Recent investments in our facilities have resulted in the vast majority of BPS facilities having air conditioning, which is crucial to keeping our young people safe and comfortable during this heat emergency. We encourage students and families to prepare for hot weather this week by staying well-hydrated and dressing appropriately.”

Citing temperatures in classrooms, school districts in several communities, including Lowell, Worcester, and Framingham, closed schools or let students out early for at least some portion of the week, citing the extreme heat. Farther west, school officials in Springfield, Chicopee, and Westfield said without air conditioning in their buildings, the unusual September heat would create sweltering conditions.

Material from previous Globe stories was used in this report.