I have a movie question that's been driving me nuts.?

Question

I've been dying to see it again as an adult, as I've seen it between 1990 and 1994 on USA's Saturday nightmares. One of the movies during this period was SLUGS, which I purchased on DVD. Another was Tourist Trap, which, to be honest, I struggle to watch but bought it for vintage purposes anyway.

So here's the movie that's been driving me nuts. It's very similar to THE SUBSTITUTE but I don't believe that it's that movie. The one I'm thinking of has a school teacher (I think) fighting off students (gang members?) inside a school.

I remember a lot of blood and gore, and ANY assistance on this movie would be GREATLY appreciated!!!

Answer 1

Years (2563)  

Answer 2

or maybe class of 1999

Answer 3

The only other movie that I can think of that fits your description is "Class of 1984."