in theory ds school does detentions, but they are incredibly rare.
they have a behaviour system where you can get a bad behaviour point. So, homework not handed in, using phone in class etc = 1, 2,3 or 4 behaviour points.
behaviour point salso mean email home to parents. 12 behaviour points = meeting with deputy head and lunchtime detention. After school detentions woudl come next.
In practise, most boys do not accumulate 12 behaviour points in a whole year. There was one boy who was getting a lot and the school's response was more in the line of support and pastoral care than punishment as they recognised that this boy was having a relaly tough time, and needed help.
That is a super slective grammar.
Our local school (comp in a bad area) recently got a new head. In her dirve to up standards she introduced draconian detentions. So, no homework = immediate detention, uniform violation = immediate detention etc.
It was very touhg, she did get a big turn around in behaviour, but it was very harsh, especially to basically good kids who made a mistake, it was zero tolerance.