When I was 15, I went with school (please remember this was 2003 so a while ago now!) and the teachers made sure we knew where and when the coach would be leaving. They then legged it off around the park leaving us to fend for ourselves whilst they got on all the best rides
Same with my school trip to Alton Towers in 2014. At the time, I think I was 13 yrs old. The teachers literally left our small group (about ten of us) alone to fend for ourselves, despite most of us having never visited the park before. We kinda lost a few people on the way around the park and the teacher went absolutely mad at us...
We had an absolutely brilliant day though. In fact, had I not gone, I'd never have become so interested in theme parks!