Hi,
My DD is at Grey Coat Hospital 6th Form, having also attended the school since Year 7.
The atmosphere for new students joining who have previously attended other schools is very welcoming. The 6th Form arrange a Year 12 'bonding' day where after a day of orientation/induction for all students attending the 6th form, they then spend the day on a trip somewhere in London - this year they went to Kew Gardens - where they are initially placed into small groups to get to know each other. My DD's experience was one of wanting to meet new people and her and her friends were very welcoming of the 'new faces' (especially the male ones 
).
Forms are mixed in the sense that they are pupils from both Year 12 and 13 which the school sees as encouraging informal mentorship and buddying, as well as creating a 6th Form community feel.
Pupils are from all areas of London, my DD's friends travel from Westminster, Hackney, Hammersmith & Fulham, Kensington & Chelsea, Lambeth, Southwark, Wandsworth, Islington...
There are a number of extra curricular clubs available to the 6th Form, both academic focussed to support studies/UCAS applications, and creative or health focussed activities (one of the sports teacher created a 6th form lunch time running club for example, at the request of a student).
As with the rest of the school, expectations on students in the 6th Form are high and the same level of strictness when it comes to effort, organisation and attitude are applied. They do treat them as young adults though, and my DD was pleasantly surprised by the clear switch attitude towards them as learners.
Results are good, there are always a number of pupils who go to Oxford or Cambridge, and the 6th Form team support all pupils in exploring Russell Group universities as ones they should aspire to. They are given guidance on the UCAS system from very early in Year 12 and are also good at supporting pupils who may take a more creative route - e.g. exploring Drama school admissions.
Hope that helps, good luck with the transition.
