When I was at horticultural college, we had mature students sharing a classroom, canteen and workshop with 16 & 17 year olds, often unsupervised by any staff member. We went on day trips together, drove tractors together and were constantly in each other's company from 8.30 to 5 every day. When a couple of us older students got a part-time job working at the college, we had to have CRB checks (as they were then) because we might come into contact with 16-17 year old students...even though when we were working, we were in a separate area from any students, and anyway, these students were the same ones we had been spending all our time with for the whole of the previous year...! It's a crazy world!