I was a secondary science teacher before I ran away to HE! I always just tested my sugars in class and when the students inevitably asked what on earth I was doing I explained.
Quite often there were diabetic students in my classes and I thought it was very important to set a good example to them and show that it's nothing to be ashamed of. I also used to inject in class if needed (under my desk in my stomach).
Occasionally I had hypos during lessons (once when Ofsted were inspecting - fun times) but would just drink a bit of the Lucozade that was ALWAYS in my desk and/or bag and carry on. Any kid that moaned about me drinking Lucozade in class would usually get an eye roll and possibly a witty comeback depending on how wobbly I felt at the time!
If you're on MDI or a pump then skipping lunch because you're too busy is no better or worse than a non-diabetic as you would just skip your lunch bolus.
It wasn't around when I was teaching but I can imagine that a Freestyle Libre would be great to have in the classroom. It would have been very interesting to see just how much my bottom set Y9 and Y10 classes spiked my sugars! Just made sure the little darlings don't make off with your reader as I did once have my Accu Check mobile nicked off my desk by a very naughty Y7 boy once. He returned it in tears an hour later because his friend had told him I would die, I didn't let him know I'd just gotten the spare from my car.
Good luck with the roller-coaster of teaching! Diabetes is no obstacle at all; it's the paperwork that's killer