Dunno, its just what happened, by the time I left even most of the teachers just called me by my surname when most people were called by their first name, there were a couple of other people that also got called by their surname sometimes. But I honestly don't know why it happened, just that it did. Felt so weird when I left school and went to uni, had to remember to introduce myself with my first name and it took a while to get used to people using it.