According to the teacher's union, he suffered multiple injuries including a dislocated shoulder and wounds to his face and hands in the attack.
A 14-year-old student accused of the assault is in police custody and is charged as a juvenile with aggravated assault.
The 60-year-old teacher, identified by police as Lawrence Williams, was assaulted inside a science classroom around 8:40 a.m. at the Leeds Middle School in East Mount Airy.
"It is what we consider to be a severe assault; something that is very numbing to hear something like this happen," Philadelphia School District spokesman Fernando Gallard said.
According to school officials, Williams, a teacher at Leeds for 20 years, was returning schoolwork to the 14-year-old student and the papers were covered in red pen marks, perhaps those pen marks noted corrections or the student's grade.
The eighth grader became angry and a verbal argument between the student and the teacher turned physical with Williams taking multiple punches to the face and body, officials say.
"So far the information that we have is that the teacher was punched repeatedly by the student," Gallard said.
"I'm just shocked that something like this would happen to such a phenomenal teacher," Benson Williams, a school social worker, said.
Student Willie Williams witnessed the assault.
"I was walking past, I saw him swing, I kept walking, but it didn't process at first," Williams said.
The 14-year-old student was placed under arrest at the school on Mount Pleasant Avenue.
Furman Pace, a father of a seventh grader, came to take his daughter out of school after learning a teacher was attacked.
"It's ridiculous that you can't feel safe while your child is in school. That's ridiculous. It's unnecessary violence. It's a shame. It's sad," Pace said.
Leeds Middle School does have two police officers on duty each school day.