I did a thread on this years back, this was something that really bothered me as a kid. I saw parents do this in public as well. Yes bathroom denial was common in my schools. In first grade our principal banned anyone going during class because someone was writing curse words on the walls. Us first graders had to get by on 3 breaks a day for about a month, surprisingly no one had an accident, but it was very painful at times. Our teacher wanted to let us go, but she wasn't allowed to.
My 3rd grade teacher once took away my scheduled break as punishment and did it to others. She finally let me go when I bursted into tears during class close to lunch time. I had trouble with her denying me the restroom the whole year. I walked out of class once as instructed to do by my parents and after that when I would ask and she would say no, she then would say "and you better not walk out of this classroom". They padded in school and I thought I would get in so much trouble if I walked out again. I had a lot of issues with her.
In private school in 4th grade I asked to go during recess and I was allowed to go, I had to go again back in class. The teacher let wouldn't let go a second time. I drank a Sprite during lunch and was bursting to go. I had to hold it for two hours and experienced a lot of pain.
I got held back in 4th grade, my second year in 4th grade the well for the school broke. When I got to school all the restrooms had out of order signs. They wouldn't let anyone go to the restroom till about 30 minutes after lunch. Some kids got dropped off early in the morning and had not gone already for a couple of hours. Yes they just skipped our restroom breaks and expected us to hold it till the well was fixed. We also didn't get anything to drink and I was so thirsty. They brought water from the outside for lunch. I remember one kid during lunch had to go bad and we were making fun of him, he started to cry. I certainly hope they didn't make they kindergartners and 1st graders wait that long!
My 5th grade teacher punished these two boys for horse playing in the restroom by not letting them pee the whole day. They were finally allowed to go by a teachers aid about an hour before school ended when the teacher stepped out. They were bouncing in their seats and all the teacher did is laugh about it. I too was denied in that class a few times, but never had breaks removed.
In middle school and high school I had a few teachers deny me as well, but I was used to holding it by then and class was only 50 to 55 minutes. This still goes on today, but I don't think teachers would get away with it the way they did back in the 80s when I was a kid. If a school denied the who school till lunch it would be on the national news. Back then nothing came of it.
My second high school your weren’t allowed to use the bathroom at all apart from 5 mins before the bell at each interval. So you could imagine the chaos of a few hundred people trying to use 3-4 urinals in that time frame. When the bell went teachers would grab students and throw them out the toilet. Eventually I worked out a few schemes morning and afternoon break I peed in the trees behind the gym block. Lunch break I got a study pass and used the headmasters toilet as it was beside the library.