In an interview Friday night, the teacher, Pewu Johnson, a Liberian immigrant with deep roots in Philadelphia and its schools, described the attack.
He said he had a run-in with his assailant early in the day when the boy behaved "inappropriately" with a female student, and he ordered him to stop.
Later, during seventh period, the teen found Johnson and angrily tried to block his way.
"He grabbed me, then lifted me up, then dropped me on my back, on the floor. I became unconscious. I wasn't hearing anything. My eyes were closed," Johnson said.
He said he had intense neck pain and was bleeding from his elbow, and ended up spending hours at the hospital.
He isn't sure when he'll be able to return to work, he said, adding that he was still quite sore.
A student standing nearby captured footage of the teacher splayed flat on the floor and posted it on Vine, a video-sharing service.
Students began talking about the incident on Twitter: "Old head got put to sleep in Bartram," one Tweeted. Others chimed in.
"This is a grave concern to us," said Fernando Gallard, a district spokesman. "The student has been suspended. He will be referred for expulsion."
Johnson said he would pursue criminal charges against the boy.
"There's a need to press charges," he said. "These things need to be discouraged."
Substitute teaching can be tough, said Johnson, who trained as a teacher and a city planner, and has been a district substitute for 14 years.
Over the years, Johnson said, "I've been abused and bullied," but Thursday was the first time he had been assaulted.
Bartram, in Southwest Philadelphia, found itself in the spotlight during the last school year for violence and chaos. In March, a conflict-resolution specialist was knocked unconscious by a student.
But the school's climate improved after the Philadelphia School District invested resources in it - more school police, a second principal, and other help.
This year, a new principal took over, focusing on enforcing rules and calming student behavior. Abdul-Mubdi Muhammad values structure.
"Mr. Muhammad has been advocating for more resources, but they haven't sent us any help," one teacher said. "A lot of people feel that this is a pressure cooker about to explode again."
The teacher did not want to be identified for fear of reprisal.
Muhammad is seen as having helped the school make strides. But "we started with a huge deficit," the principal said. "When I came into this building, we were" way behind.
Improvements have been made over last year, another staffer said.
Students used to openly smoke marijuana and cigarettes in the school, and that has largely stopped, said the teacher, who also declined to be named.
But the lack of staff is a problem.
"They call for hall sweeps on the loudspeaker, but there's nobody to sweep the hallway," the teacher said. "There's still ample students walking the hall, and ample fights."
The earlier assaults on staff put the school on edge.
On Oct. 21, a teacher was pushed to the floor twice by a ninth-grade student who attempted to snatch the teacher's laptop. The teacher's back was injured.
And on Oct. 9, a student punched a teacher in the face. A fight among students had erupted outside the teacher's classroom, and one young woman wanted to go outside to watch the fight. When the teacher attempted to block her from leaving her class, a 12th grader struck the teacher, who was treated by the school nurse.
After the major problems last year, 10 school police officers patrolled Bartram. Now, there are three for the four-level school building and its 1,000-plus students.
Muhammad, a former Olney and Masterman math teacher and charter-school assistant principal, said he was intent on rebuilding Bartram.
"We're trying to develop a culture here," he said. "We have to rebuild the idea that this is an academic setting, that no, you can't do that thing you could do last year. There must be visible consequences for everyone."
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