I switched 6th form in April of year 12 from a grammar school 15 miles away to a comp school around the corner. My AS grades suffered immensely as the course the comp school were doing was different from the one I had begun on and so I had to self study pretty much everything. I had trouble in terms of the social aspect because at my first 6th form I pretty much knew and spoke to everyone, and at my 2nd 6th form I knew a very limited amount of people. I ended up dreading going to school and pretty much bunked everyday getting into quite a lot of trouble. My AS grades were not great, but I don't regret moving because at the beginning of year 13 I decided to change my attitude and not care if I was alone at school all the time and did much better at A2 than I would have done had I stayed at the first 6th form. It certainly was an emotional rollercoaster, and moving 6th form midway through your course equates to a lot of admin work but, depending on your reasons, it may well be worth it.