At first I thought it might have been used as a BBS, hidden out of sight during the day and administered by a teacher/SysOp during the evening. But if it was, it was short lived or not open to non-students, because I never heard about it, and I wouldn't doubt that I called every local BBS at least once.
Also, that's pretty much all my school had too, was IBM. I switched school systems in 1989, and though my new school was better equipped than my old one, I mostly used the same IBM computers from my first day of school until my last. I think they were known as the Model 25? It was the all-in-one Mac looking PS/2.
They were still in use when I graduated almost 10 years later, although the school had added about a dozen Win95 machines by then, low end Pentiums or possibly high end 486 machines. If memory serves, they were generic beige boxes from a local system builder. However, with so few machines available unless you had a pressing need for the GUI, you ended up in the old lab using DOS on the PS/2.
I heard from a younger student they were still using those old dogs as late as 2002, which doesn't surprise me at all. As far as I can tell, my school had an aversion to getting rid of anything, since every classroom had at least one Commodore PET or Apple II collecting dust. Would be kind of amusing if they were still sitting on a few of those...