I don't know much buses but I definitely know there is a sign on trains stating that any school kid travelling on a fee pass should vacant seat if there is an paying adult standing. Hardly ever see this gesture extended to anyone. And many times school kids have their legs stretched abd rested ib teat n frnt.
This I find quite common.
Sometimes it cannot be helped; on a crowded train sometimes the kids are encroached into their seats. Making them get up and having an adult try to take their seat is genuinely awkward. Moreover is when an adult refuses to take the seat vacated by the student, again very awkward.
Adults also feel relatively apathetic and/or embarrassed to tell students to give up their seats. And if it hasn't quite ticked on anyone here, kids actually find it somewhat amusing and "satisfying" (can't find a good word here) when they attract the attention of a berating adult. They just laugh, quietly remark "what's his/her problem" (in their minds: referring to that old hag/d***head) and may or may not comply. In short, you haven't achieved anything except lose some face.
Misbehaviour is typically reported to schools, but most schools try and wash their hands of responsibility (it can't be our student, how can we possibly make students follow the rules, etc.). I've reported ill-behaviour to a couple of schools and have got the latter response, i.e. completely washing their hands of responsibility with little regard that the students are tarnishing the good name of the school.
There are rarely any guards/ticket inspectors on trains (almost impractical in the peak hour) to monitor and check on this kind of behaviour.
Moreover, I've gotten quite used to never having a seat (notwithstanding having a job which is in front of a computer for hours upon hours in a day), so most of the time I do not bother unless I am really tired. I do get highly annoyed by students who insist on standing where they are just to have a chinwag with their friends, not realising that there is space in the bus/train carriage that could otherwise be occupied by ever boarding patrons that is rendered relatively inaccessible due to their not moving. This gets particularly annoying when a bus driver is apethetic about this and declares a bus full, thus missing passengers along the way, although there is space for at least 6 passengers (but the space is at the back of the bus).
There is absolutely no excuse for kids - or anyone for that matter - to have their feet on seats. Again, however, enforcement is lax and apathy on part of the fellow pax to tell the offender to stop infringing is ever present (with the exception of a crowded train).