I have four Grandchildren at School , they may not always get along with their teachers but they know to have respect for them - very little bother at any of their (3) schools.
I live in a block of nine flats, seven of my neighbours are younger than I am by some way - all are courteous,helpful and ready to do odd jobs, shopping or whatever I need.
Yes I've met some snotty teens but I've also met some obnoxious older people too - some have been downright awful.
None of this takes away from the horror of the attack in the OP, but I state again , it's the minority that grab the headlines.