I guessing, but it looks like the parent-teacher conference resulted in the student being punished in some way, loss of cellphone, etc. and the student decided to punish the teacher for his giving a bad grade to the student.
Now, here in my county, the student would be automatically expelled from the public schools system for attacking a teacher, and if under age 16 be required to take classes at a separate county school for ‘bad students’ where the parents are required to provide transportation, etc.........................
I believe this is already the school for those students.