My kids secondary school doesn't give detentions for year 7s for the first month.
After that if a child doesn't have any of the right equipment like red pen, green pen, blue pen, highlighter. reading book, eraser, etc, it's an automatic detention.
One of my kids didn't have a green pen with them once towards the end of year 10, first time ever. They actually had 2 in their pencil case for the first two lessons so think someone must have taken them. Even after almost 4 years of always having equipment and being a model pupil, there was no leeway from this teacher and she gave my child a detention. This is despite teachers fairly often forgetting class books and other things, not marking tests correctly. forgetting they have set homework etc. They expect absolute perfection from children which I feel is damaging but are often far from perfect themselves.
Anyone can forget something occasionally, we're not robots.
Anyway, my child was upset and their form teacher stepped in to get the detention removed. If they hadn't, then I would have. If my child didn't have equipment often or was not doing homework or was misbehaving, then I would agree with detentions, but I can't stress how much of a rule follower they are. Not having 1 pen in 4 years while being otherwise a model pupil should not call for a detention. My child didn't need a deterrent.
I'll be glad to see the back of the school when my youngest finishes this year. These rules with zero leeway make some kids terrified and anxious, constantly checking things, worrying and striving to be perfect, it's not healthy. Then seeing many of the teachers be fairly poor at the things the red kids get detentions for very frustrating.