Sixth form boarding school for anxious expat?

TBH I think you need to question your decision about boarding for an expat child who appears quite vulnerable. Things may escalate for them if they are away from their family. I would agree with HG that pastoral care is important and that you should check to see if there is a full time child/adolescent counsellor on site and not just one that schools contact if there is a problem. I believe all schools and especially boarding schools should have this provision. And yes free of charge. Also it is not easy to send a child home to their parents in another country and its unfair on extended family to assume responsibility for this. I would advise you think this through. Exam anxiety and perfectionism now may develop into something else later and schools are often too busy to notice until the issue becomes more pronounced by which time it's usually quite critical.

Another vote for one of the Quaker Schools - Leighton Park.

"My own children and others I know are at these schools and all are v happy with them - academic, co-curricular, social, pastoral, so can recommend"I know personally and professionally parents and children at most of these and I know most are very happy with the school and pastoral care in particular a few are not happy with the pastoral care. Ditto DS2's school.
At very school you'll find parents who are delighted with their choice and absolutely believe in what the school offers a few who will cheerful regale you with their personal horror story be poor teaching/inadequate pastoral care/too pushy/not pushy enough etc.
Pastoral care is complicated its very personal and a child/parents experience will be very much affected by the individuals they meet, how you get in with them and if you are coning at the problem from the same place. Parents do need to remember that boarding schools/staff have a duty of care not only of an individual child but also to all the children in a house/the school. IME parents can get frustrated when schools send home children who are have depression/high levels of anxiety/ significant OCD, eating disorders or are claiming they're suicidal and can accuse a school of over reacting or not caring. But its not that the school dont care but teachers are not mental health specialists, boarding schools are exactly that not branches of CAMHs therefore cannot offer the required level supervision and expertise that these conditions can require and as I said they do have to think about the other pupils in the school, for example a suicide in a boarding house will have very serious long term implications for the other pupils. As Derek says HMs also often have a significant teaching responsibility as well and really struggle to b available for struggling unhappy individual children and their parents 24/7 day in day out. This is why IMO if very high pastoral care is essential do enquire into the existence of residential matrons in a boarding house, counsellors (which should be free) therapists and trained and knowledgable staff in the school medical centre 24/7.

How about Gordonstoun? Not many people know that it is the birthplace of the Duke of Edinburgh's Award. The Week magazine voted it best for 'All Rounders' in their Autumn edition of the independent school's guide. It is also the founding member of the Round Square group of schools which all share the same holistic approach to educating students as a whole. Have heard that it is really strong pastorally. Also heard that they have a healthy mix of nationalities. Altlantic World College ethos was based on Gordonstoun's as both schools share the same founder (Kurt Hahn). Hence their emphasis on service to the community, outdoor education, sailing and of course strong academics.

Another vote for Bootham in York. A friend's child was transformed by their time there.

I hope you find a suitable school for her,
I love happygardening's comment about the teaching hours. In fact I think it should be a question asked by parents when visiting a school. Some of the teachers I know have had a ridiculous number of teaching hours. They really struggle to run a House too.

I second the PP who said that schools may already be full. Places are given out in January and we are now nearing the middle of March. You may be limited to which school still has places available.

My own children and others I know are at these schools and all are v happy with them - academic, co-curricular, social, pastoral, so can recommend (they are in alphabetical order):

Abbots Bromley
Abbotsholme
Abingdon
Cheltenham
Fettes
Pangbourne
Radley
Repton
Sevenoaks
Shrewsbury
Uppingham

I can't share my 'don't recommend' list as that wouldn't be fair as they might be based on individual grievances. But I would say, schools can change with fresh head, new staff, so any recommendation/non-recommendation should be viewed in this light. Enjoy choosing!

How about Rochester Independent College? Our daughter is there (not boarding), and she loves it. Great caring staff, and a good fit for kids who don't necessarily fit the 'normal' mold (DD is dyspraxic).
Small classes, informal atmosphere with no uniform, a slightly hippy vibe (!), but work is taken seriously. They get very good results without piling on the pressure like some schools do. Best of all - no entrance exam!

King's Canterbury is a great school. Boarders are full boarders and are the majority with a small minority day pupils. Lots of ex pat children who fly all over the world to go home in holidays. Problem for you is there is a competitive entrance exam for sixth form entry

Uppingham state on their website that they Pre test for 6th form entry I suspect most schools similar to Uppingham will do the same. Many of those you mentioned will take new pupils into their 6th form often from abroad with high grades at (I)GCSE ; As and A*'s to improve their results. Often grades stated on websites are the minimum requirement and entry can be very competitive.
If your looking for a place for this September then you're going to have to start ringing around as I think you'll find many have already offered all their places.

Marlborough definitely have entrance exams as does Rugby I believe. I think you have to be relatively tough to enjoy Marlborough. If you are then you will have a fabulous time.

I am not sure whether this is helpful or not but the Good Schools Guide produces a guide specifically for boarding schools. However, you may already have enough to think about.

Regarding the query about Kingham, I believe it takes quite a high proportion of lower achieving children and prides itself on a slower pace. Therefore academic children just don't go there. If your child needs a slower pace, then it is a good choice. If not, they could be bored.

I've no idea how they would be for 6th form spaces but I'd suggest Cheltenham College may tick a lot of boxes on your list. A bit further from London but certainly has expats/overseas students / London families and I think decent numbers in every weekend.

Good luck in your search and I hope you find a good fit for your daughter.

Just a method suggestion. E.g. With our dyslexic son who was going to board from overseas at 13 we made a chart with all the factors we wanted to consider, distance from home and airport, weekend arrangements in school, number of exeats, sport, art, pastoral care, dyslexic provision (we found many schools gave lip service but didn't care about it really). The list was different according to each of our children's needs. We then accorded each topic a category according to its importance so being near an airport was A for us. And then each thing got marks. We are not very mathematical but having some way of quantifying was very helpful. At 16 your child
will also have strong views which you should
listen to, even if they're a bit daft, our DD didn't like the long skirts at one school and did like the uniform at another! But they will
get a feeling. DD really liked Wellington for 16+ especially the choir but was put off by the entrance exam and its reputation for the girls being ranked 1-10 and it being full of petite blonde sloanes.

Ok I'll be a bit more specific. At an improving pastoral care at boarding schools study day I am once attended there were staff from big name X Y Z , not so big names J K L and non big name A B C when we all sat around comparing notes (as you do at these kind of things), it became pretty obvious that all were very committed to high standards of pastoral care, this is what parents want and expect regardless of what they're paying. None said or implied they couldn't care less about their pupils although some definitely had more of what I'll call a man up culture than others. It also became pretty obvious that wealthy big name schools were in general able to employ more teaching and non teaching staff often with specific pastoral roles, e.g. a senior member of the teaching staff whose main role is to be responsible for pastoral care, three or four counsellors, therapists, residential matrons, specially trained nurses (on duty 24/7) etc and that schools who weren't as wealthy were simply not able to do this. Also as I said above in many schools particularly smaller schools who aren't as wealthy as the big names and may have less staff HM's will also have a full teaching commitment. Providing high standards of pastoral care is time consuming and also it can be even emotionally draining, and I know from working with my teaching colleagues that if you've been up all night with a suicidal pupil you struggle to skip off to teaching your morning math class. It's quite simple big wealthy schools with matching fess have the money to pay more staff.
I'm not saying small non big name schools with low fees offer crap pastoral care but contrary to what many think on here big names wealthy schools are able offer excellent pastoral care.
OP you need to look at each school individually.

Still Happy I don't subscribe to your generalisation

Sarah like you I write from my own experience of both working in "big names" and having a DS who went to school one. We found the pastoral care at DS2's school to be absolutely outstanding his HM was frankly brilliant.
Through work I attended training sessions and met some staff from "non big names" as a general principle when it came to pastoral care they weren't doing more that we were and in fact they were often doing less due to more limited resources for example many small boarding schools don't have resident matrons but these can play a very important role in pastoral care as they are not part of the teaching team and therefore have a different relationship with pupils.
I can't comment on Sevenoaks pastoral care as I don't know much about it but I do know parents who's DC's are/have been there and talk very highly of it in general.
I think it also has to be acknowledged that it's perfectly possible for two children at the same school big name or non big name to have completely different experiences whether this is academic or pastoral care. Much of ones experience of a school's pastoral care very much depends on the individual staff you come into contact with.

Try Seaford College, West Sussex.

Very strong pastoral care, non selective but on the up. New head a couple of years ago and pupil numbers have risen 25%.

Still maintains its lovely atmosphere though.

I am paying 24k a year for a non 'big name', I really don't think that the fees or how the chattering classes revere them is indicative of their pastoral care.
I have a nephew at Sevenoaks and one in Tonbridge, I really don't think that Sevenoaks is in any way suitable.

"Went there for 6th form and the girls were ranked out of 10"
"I'm pretty sure girls get rated out of 10 at every boarding school"
I'm not denying that this sort of thing goes on at many boarding schools it's inevitable when teenagers live together but it also goes on in day schools, youth clubs, scouts cadets etc so it certainly shouldn't put you off boarding. I worked in the private sector and was really pleased by how caring the majority of pupils were of each other.
IME of "big names" is that they can offer excellent standards of pastoral care they after all have the resources to do this staff are significantly less stretched, DS2's HM for example barely taught any lessons, his job was to look after all the needs of the boys whether they be academic or pastoral in his house. Parents paying the sort of fees "big names" are asking now have very high expectations of not just academic performance or sporty prowess but also pastoral care most parents don't want cold showers and keep a stiff upper lip and think of England ethos anymore. Small schools often just don't have the resources to do this. I would find out about things like are matrons fully residential in boarding houses and other what other staff residential AHM's tutors etc? Also opening hours of school medical centres and the qualifications of staff on duty especially at night. All of these can play a very important role in a boarding house/school and in pastoral care in general wealthy "big names" can afford to not only employ these staff of the right calibre but house them on site/in boarding houses.

Another vote for the Quaker schools, especially Bootham, York. 90 minutes from London on the train. No exam.

I'm pretty sure girls get rated out of ten at every boarding school FYI
They certainly did at mine and at many others that friends attended.
We also rated the boys!