I work part-time in concessions at a large repertory theatre (stage plays, not movies). During the school year we get frequent and immense school groups, mostly middle school and high school age. We dread them because they are loud, rude, indecisive, monopolize the counters and cannot grasp the concept of ordering one at a time. I'm sure that individually they're mostly lovely children (children at the theatre with their parents are almost invariably well-behaved), but in herds they're just not fun.
So the other day I was not terribly enthused when I saw a school group consisting entirely of boys around the age of 11 or 12 approaching my counter. I was braced for the usual mayhem, but instead EVERY boy was polite and respectful, saying "please", "thank you" and ordering one at a time. I was utterly amazed, and wished I could have located a teacher or parent to express my pleasure at serving a well-behaved group, and to ask what they did to persuade them to behave like that.
I guess it goes to show that children can observe good etiquette if they're expected to. I imagine the boys were simply expected to behave well, and that misbehavior was not tolerated at whatever school they went to. Whatever it was, it was great, and I wanted to share my good etiquette experience with you all!