I went to public schools in the 70s and 80s and never saw anything like this. I assume that a "supply teacher" is a substitute teacher. I think kids do tend to take more advantage of a substitute teacher than they would a regular teacher though.
That was my thought as well. Not that these little turds weren't way out of line. Good Lord. This woman's classes sound like that Cheech and Chong routine "Sister Mary Elephant"...
"Young man, give me that knife."
"ThhhhhhhhWACKddddd!"*
"Thank you."
*[SFX of the knife being thrown at, and sticking in, the blackboard]