I'm not sure if this existed outside of my hometown, but I know at least my rival high school had the same rule as the one I went to. It was this thing called Sweeps where the idea was that once the final bell rang, teachers were to close their doors and refuse entry to any students for any reason. Teachers and faculty not currently teaching were to roam the halls and 'sweep' anyone they saw to the cafeteria where you wait in line to use the phone to tell your parents you have in-school-suspension for not being in class.
Here's the big problems that came up: 1. Traffic through the hallways was already a problem. I would always get to class with maybe a minute to spare, tops. I carried everything with me because I knew there was never time to use my locker, and never time for a bathroom break. Since a lot of teachers insisted you use your 5 minutes between classes to use the bathroom and wouldn't let you go during class, I had to be sure I could hold it all day.
For a year and a half my school was under construction, moving the library and adding a whole new wing. This meant that one of only two corridors connecting the North and South halves of the school was inaccessible. If you had an art or P.E. class on the North end and a class on the second floor (which would be the South half), you had 5 minutes to get your stuff, mosh your way through that one hallway, book it up stairs, and then rush through the second floor halls to get there in time. Even then, you might not make it.
Zero tolerance was taken to ridiculous extremes with this rule. We had to wear ID badges with really shitty lanyards that broke easily. Frequently the part holding the badge would break and the badge would fall off and you might not notice until later. Twice in this one class I took, in the same semester, someone's ID badge fell off in the hall right outside the classroom. The first time you could even spot it from the little window on the door, just laying there while the hall was empty. The teacher refused to open the door to let them get it because Sweeps and rules are rules, and instead wrote them up for not having their badge present because rules are rules. The second time it happened, this girl started crying because she had never got in trouble at school before and was terrified about her parents finding out. She was sent to the office for being a distraction and refusing to participate in class, even though she just kind of quietly sobbed to herself for like 40 seconds before she was made to leave.
3b. Kind of a follow up with my own experience. I once threw up on myself during class and my teacher sent me to see the nurse; he didn't write me a note or a pass or anything he just told me to go. I figured the fact that I was pale as a ghost and wearing a shirt covered in vomit was as good as a hall pass, especially since the nurse's office was two doors down and just around the corner. Nope. Just as I was turning the corner, the fucking band teacher 'swept' me. Literally said, "I don't want to hear it," when I said I threw up and pointed at the evidence. I was escorted to the cafeteria, waited in line for the phone, and when it was my turn I got my mom's voicemail where I only left the message, "I'm suspended for trying to see the school nurse." I glared at that teacher the whole time, trying to urge myself to vomit again just to make a point. After I made the call he let me go to the nurse who then sent me home so I didn't have to serve out my punishment.