We've been to see one 6th form which is a great school but the grades are not quite as good as Dd1's current (admittedly highly selective) grammar school and the journey is slightly longer. As she already travels nearly an hour a day, I don't think she'd want to increase it. But it was helpful in helping her decide what she wants to do. Her own school's open day is next week.
Annoyingly the other 6th form we wanted to go and see has its open day on the same day she has another commitment. This one is definitely a bit less academic but in a really nice area so that makes it appealing.
We may put it down anyway as a back up in case but realistically I think she'll stay at the grammar.
@eurotravel the harsh approach of some 6th forms is interesting and I think goes up from the academy approach at secondary. There are a few around us - the London Academy of Excellence springs to mind -that have strict dress codes and attendance and are in reasonably deprived areas but get amazing results. I have a few friends whose kids have chosen them, they tend to be very good for Stem subjects.