The schools were dismissed at 1:30 p.m. with routine transportation for students.
All afterschool programs were cancelled.
Updated information is posted on the District's Information Hotline at 215-400-INFO (4636).
The Archdiocese of Philadelphia also dismissed schools at 1:30 p.m. on Thursday.
The National Weather Service said temperatures could top out at 100 degrees Thursday. That's after temperatures topped out at 97 on Wednesday, topping the previous record by 2 degrees.
By this afternoon it was so hot even the golfers stayed home and away from the range Fairmount Park.
"It's been affecting it," said golf course manager Henry Stone. "I'll say that. Very slow."
Can it ever be too hot for ice cream? Maybe today. At Chloe's Corner in Manayunk, Action News found very few people stopping in for a scoop.
"I think it's too hot," said Nicole De Luca of Manayunk. "People don't really want to come out, because we've been kind of slow."
But there was no slowing down Richelle Lindsay of West Philadelphia at midday, with temperatures climbing toward a hundred degrees. She still got in her exercise on Kelly Drive.
"I already jogged five times this week so I am just going to walk today because it's extremely hot," she said.
Earlier, at noon, Action News found the temperature to be 95 degrees and rising on Independence Mall. But the high heat didn't stop students from the Hartford School in Mount Laurel, N.J. from heading to there for their fifth grade class field trip.
"It's a walking tour of Philadelphia in 95-degree weather," said Carol Alexander of Mt. Laurel, N.J., part of the group.
It was a day the students had been looking forward to, after all. So they just came prepared.
"We're drinking a lot of water, finding the shade and trying to stay in air-conditioned places," said one student.
Another tour group was in town from San Francisco. And boy, the heat was a shock for them.
"San Francisco is very dry heat. It's all wet here. I feel all sticky. I don't like it," said Zaire Johnson. Asked how he was coping with the humidity, Zaire replied, "I bought a hat and just swagger in it."
It was a slow day at Penn's Landing in Philadelphia. There was a little work going on, but generally a sparse crowd. Those who did venture out sought coolest areas they could find.
"Right here I've got the waterfall," said Tiandre Richardson of Germantown. "Since I couldn't be down there [closer to the river] because it was too hot, this is as close as I could get to the water, hear the sound and relax."
An excessive heat watch was in effect through Thursday evening for much of southeastern Pennsylvania, northern Delaware and the western part of central New Jersey.