I know a lot of the Channing girls. Some have been there since tiny, some joined late and some who left before 6th form. It is a brilliant school, very supportive. My best friend who went there had a lot of health problems at one point, and had to spend time in hospital with ops etc, and they made a real effort to help her re-settle when she came back. The small class sizes are wonderful, and there is lots of personal attention. There is quite a range of girls there, but mostly lovely with good manners and social skills. They often spend a lot of time together outside of school, especially with great coffee/food places so close for after school, which is great, and as they get older they tend to get to know the boys (and girls now) from Highgate. As the years are so small, made up of about 60 girls, the community feel is great and the girls tend to know and socialise with girls outside their years as well. Most of the girls acheived very well in GCSE, and same at A Level, and the couple that got lower than predicted simply didn't work hard enough consistently for themselves and the school had warned them and their families they weren't, so that wasn't the school's fault. I would say most of the girls there are pretty arty, especially as they progress, lots of music and art and drama, and there is a relaxed feel as well as that extra push that gets you reaching your best. It also develops independence gently but surely, unlike many of the private schools even in CoL. For example, they do very helpful things for outside of school as well, like having a babysitting register for the older girls, so that parents of younger children can find someone they trust, the younger girls have someone they often know (even if only a little) and the older girls learn responsibilty and earn a bit of money on top!
Hope this helped give some idea of what they encourage in girls.