6th form was part of secondary school and within walking distance. Most of her friends went there but they were starting to go into smaller, bitchier groups. Had to be in uniform (suits), shoes of a particular type for girls. School was too involved and there was no freedom for personnel growth or responsibility. Even free/study lessons had to be taken on school grounds, had to stay there for lunch, so either school dinners or packed. Had to be 9 to 3.30pm every day.
College was a bus ride away so involved learning about timetables, money budgeting for bus and dinner. Able to leave college during free lessons to wander around city shops. Only had to attend actual lessons so might only go in 2 hours on a thursday, nothing on a Friday for example. Could wear what they wanted. Was expected to be in charge and responsible for attendance, notifying absences, studying, discussing any problems with work and not wait for teacher to notice first. Basically had to be grown up.
Since DD wanted to go to university after I persuaded her that college would prepare her better for the real world and going to a different city/University by herself while 6th form was in a childish bubble in comparison.
After a year she had outgrown her 6th form friends. She didn't need handholding and worked out a lot of problems by herself, eg getting on a train by herself, staying overnight in a new city, budgeting for it all. Getting a parttime job etc etc. One other friend went to the same college but different course - she outgrew the school friends too.
It really was the best thing for her.