Another Philadelphia public school teacher was assaulted by a student today - the third such attack on a staff member on school property this week.

This morning, a Northeast High teacher was punched by a student who wandered into his classroom on the last day of summer school.

The incident happened at about 10 a.m. at the Cottman Avenue school. The unknown student - who may not be a Northeast High pupil, officials said - walked into a classroom he wasn't permitted to enter.

It's not known what sparked the confrontation, said Fernando Gallard.

"They got into a verbal disagreement, then the assailant punched the teacher," Gallard said.

The male student ran out of the classroom and out of the building. He was not apprehended.

The teacher was treated by the school nurse, then taken to the hospital. He sustained injuries to his eye, and his glasses were broken.

Philadelphia and school district police immediately began an investigation, interviewing the teacher and student witnesses, Gallard said. The investigation will continue through the summer break until the student is found, he said.

If the student attends a district school, he will be suspended and referred for expulsion once he's tracked down.

"We're hoping that once the assailant is caught, the teacher will file criminal assault charges," said Gallard. "We are taking this very seriously."

On Thursday, three students at Kensington Culinary Arts High were expelled after they attacked a pair of school police officers who ordered one to stop walking the halls.

That same day, a student at Benjamin Franklin High was also thrown out of summer school after he attempted to assault a teacher who caught him cheating.

Earlier in the summer, a Northeast High school police officer was taken to the hospital after a student "mouthed off" at her. The student was ordered to leave the building and ultimately hit the police officer.

It could not be determined today whether the recent spate of staff assaults represents a spike in summer school violence; Gallard said figures were not available.

Overall, for the school year that concluded in June, violence was down by 14 percent, Gallard said.

Still, the school police officer's union has called the attacks against its members a crisis. Union officials have also asked for more and better training of school police, and said they are in talks with the district to take other measures to quell violence.

The state auditor general is also surveying school safety at city schools.

Gallard condemned this morning's attack.

"This isn't something that should happen in any way, shape or form," he said. "This is an assault on our school, and it's not going to be tolerated."