I'm pretty sure we couldn't use them for exams, either, but they came in handy for homework and everything else. IIRC the exams included log and trig tables. In college I think we were allowed to use them. But slide rules were definitely gone before I started high school, at least as far as teaching kids how to use them. Slide rules aren't the only thing which stopped being taught at schools. They stopped teaching cursive writing and using manual typewriters a while ago simply because those skills aren't terrible useful or relevant in today's world. Honestly, they weren't terribly relevant even when I learned them. I wrote faster printing and it was more legible. By the mid 1980s PCs were making manual typewriters obsolete in business settings, even in more affluent homes.You had it way too easy. In the latter days of my education I had a 'scientific' calc, but we weren't allow to use them. Get caught with one during an exam and that would get you a trip to see the headmaster! They wanted us to have that background / depth of knowledge, and in retrospect, is was probably good - although it would be overkill in 2021. When I graduated I went to work for TI and had my revenge, but then moved on to using HP when I discovered RPN. Gotta give the slide rule credit though, it ALWAYS worked - high reliability device! Speaking of reliability, I still use my HP11C regularly and it's within reach as I type, so I guess it's been as reliable as my slide rule so far. I'm still kicking myself for leaving my HP16 at a job I left hastily though. Slide rule don't do binary / hex very well.
The primary reason for not allowing calculators on exams back then was because they were still expensive enough that not everyone could have afforded them. The kids with poor parents would be at a disadvantage doing exams, so to make things fair nobody could use them. Of course, within a few years after I finished high school scientific calculators dropped in price to well under $50 and they began to be allowed even for exams. Here's some background on calculators in classrooms:
Arguably one of the most controversial pieces of education technology to enter the classroom has been the calculator.
BTW, just as an aside, slide rules stink if you have CTS like I do. It's easy enough to punch numbers into a calculator, but holding and trying to move a slide rule in small increments ends up hurting in short order. So does writing with a pen. I can't really use a smart phone effectively, either, for similar reasons. I find the touch interface extremely awkward and error prone. It sometimes takes me 10 minutes just to log into my bank's website because the password or username doesn't get entered properly. I got a friend's old Samsung S5 to play with as a gadget. I don't have cell service but I can go online with wifi. I rarely use it because I find the interface so annoying. I'm probably a rarity these days in that I don't even know how to send a text message but I've built PCs from scratch and can program microcontrollers in assembly.