At least in private schools, everyone goes to the same school, from pre-scholars to 11th graders. Unlike the buses in the USA, most schools don't use the yellow cheesewagon. They use public buses, which are usually some shade of green. They all have different interiors, so depending on which bus you take, within the same school you have a bus with curtains, comfortable seats, radios, and tinted windows, and buses with plastic coverings on chairs, broken radios, and windows with mildew growing on them. So being on a good bus is important to students.
Friends compare buses, and rejoice when they get a good one.
If you don't, it is considered extremely rude. Teachers, usually 2 or 3, get on the bus as supervisors. They sit on the front of the bus, and assign seats to people. If you talk to much, to the front and be prepared to sit with the little ones. If you don't give the teachers any problems, you are free to sit in the back.