I taught a few semesters of high-school photography a couple of years ago, and TBH, the only way I had any success in teaching my students about the importance of learning the many nuances of making a proper exposure was when it came time for them to print their shots in the darkroom.
I even tried telling one of my classes that they more than likely didn't want to bother themselves with film, but the "romance" of watching their prints emerge from the chemistry (not to mention the possibility for pinching bums in the DR) made it so that every class I taught was film-based for the majority of the time we had (although I still made sure we covered the basics of digital, since that's the world these kids really are living in)..
As predicted, they were too busy "texting" eachother in class to be bothered with ROT, DOF, and making proper exposures.. but in the darkroom - with the images emerging before their eyes - it was all "why aren't my pictures turning out the way I thought they would?" And it was a piece of cake to get them to understand why those things actually matter no matter what medium you're using..
I always found that in the digital darkroom, the degree of freedom one has to correct one's "mistakes" made it much more tricky to properly communicate just why it's important to understand what these fancy cameras are deciding for you when you point-and-shoot them.. and why it's still important to pre-visualise the image (at least to some degree). Plus you chew up classroom time explaining things about PhotoShop that are best left out of a "photography" course -- no matter how useful they may be.
And then there was the fact that cheap digital SLRs were/are still a relative novelty, which only compounded the problem; the kids who had the entry level DSLRs were always too busy fiddling with the menus and poorly implemented controls to be concentrating sufficiently on the process of making their photographs, and thus spent all their time shooting in "P" mode.. and wondering why their photos weren't turning out the way they thought they should.
The "manual" kids, OTOH, didn't have a "magic" setting, and therefore had to keep it all in play,. They inevitably had a much better time as a result (maybe this is merely an indication of my inadequate teaching skills, but I honestly think there's more to it than that )
So I'm backing the recommendation for K-1000s. I haven't looked recently, but I'd certainly go to Nikon FMs if they're price-competitive with the Pentaxs.. back then, I thought used MF NK lenses were a bit too pricey for rank amateurs.. Maybe things have changed though.
But if the course requires a film camera, K1000s are cheap and reliable and there are lots of decent lenses out there to mount on them. Heck, kids buy sneakers for more money these days! At least 5 of my students bought them for those classes I taught, and all of them wound up loving the camera at the end of the course (although I did manage to convert one of the more serious shooters to a Spotmatic/Takumar setup, which is still a much-loved combo of my own).
Sure film isn't free, but every lab I approached was more than happy to offer a special rate to my classes based on the guarantee of actually having something to run throught the machine , so it wasn't prohibitive either...