Private schools without the pressure

Nearly all independent schools are likely to have high expectations in relation to the ability of their intake. This is one of their key selling points and this is how they market themselves. The less selective ones talk about value added the top one the % off to Oxbridge/Ivy League. Most parents paying school fees want better exam results than they think their DC would have got out of the state sector. So there is always likely to be pressure from either home or school or other class mates. Very bright children at less academic school could feel under significant pressure from school because these schools want these children to do really well, so that they can say on their website open days etc so and so go 3 A*'s and went to Oxford to read English, where as the top academic schools are less likely to focus on and maybe put pressure on a couple because they've got 50 or so who they're hoping will achieve this.
It is so so highly likely that in the boarding sector that the overwhelming majority of parents are going to be pretty wealthy, DS2 school has approx 15% on bursaries and that a lot for an independent boarding school that means 85% are paying £35k pa out of their after tax income and having paid their other bills mortgage food life style etc. So those on bursaries aside your unlikely to find many parents living in small semi's in Dover on the average wage paying boarding fees. Having said this some schools are known to be very smart and have very wealthy parents, our friends whose DS had a rough time at Bedales are in fact very wealthy but said the school has quite a few very wealthy celebrities' children there, didn't bother them but some it might. Marlborough is also known to have very wealthy and smart parents. So much depends on how you as family feel about it, from my own experience most children don't care, those that do are generally disliked by all, there will always be ghastly parents at any school but at senior school you have significantly less contact with them.

Another vote for Kings Rochester. Not a hot house but gets good results and set in a lovely historic town but still with good transport links. Can be in London within half hour.

Woldingham sounds good for you. It is girls boarding and Catholic. It is just inside the M25 on the train line to Victoria/London Bridge.
It is successful, but not highly selective.
Sounds like it ticks all the boxes and is nearby too.

Take a look at Mayfield in East Sussex. RC and nurturing.

I see someone up thread has mentioned Emmanuel. Friends DS goes and it was chosen specifically for the pastoral care. We live v close and my DCs attend summer camp there. The facilities are wonderful. And am aware it has great drama and sports. Worth a look maybe?

I loved St Bedes.

King's Canterbury, while lovely, does have a rep for the children being competitive which may mean they pressure each other.

I think 'country' schools are a good call. Clayesmore?

Brighton college is shooting up the league academically so I wonder if it might be getting competitive, but it does have a good pastoral reputation. I'd definitely look at Benenden and possibly kings Rochester. Kings canterbury a great school but might be too hot-house for you.

Stowe fits the bill for your DD if she wants drama, music, art and no hot housing, excellent Head. Truly mixed ability and mixed backgrounds. All these schools have some mega wealthy parents but they are not in the majority. Brighton College and Hurstpierpoint (weekly boarding only) both have excellent Heads too. The Bradfield Head is going to Eton so there is a question mark over who will take over there.

I am aware Queenswood in Hertfordshire is recommended in The Good Schools Guide for Drama and music is valued too. Not the highest results but very good and not so difficult to get into. However, please understand all boarding schools have very rich parents where they don't just have a holiday in Barbados, they are likely to own a house there. Boarding does enable children to mix with a variety of children and make friends that last a lifetime. It suits very many children.

For all girls definitely Benenden , for co-ed what about Oakham or kings Canterbury

Leighton Park? It is a quaker schools so liberal and creative

OP said she was interested in London (day) and SE (boarding).

Wild that stretch to the south coast, and maybe Brighton College or St Bedes in Eastbourne on a weekly boarder basis?

I'm surprised that bryanston and ampleforth have been mentioned. Not because they are bad but because they are full of the very wealthy. Ampleforth is catholic so good choice but long way away so could be isolating if dc does not like boarding.

I've been advised in the past not go rise to Jane's tedious comments about boarding difficult as it is, I would advise you to do the same.

I've no axe to grind either way about Ampleforth as I'm definitely not catholic and Im ignoring Jane's predictable comment on boarding. Amoleforth has 600+ children aged 13-18 on its register so an average size for a boarding school not a small school and 75% got A's or B's at A level which is pretty respectable for a school that's basically almost non selective.

Jane two of my siblings boarded, one loved it the other liked the freedom but did n't do particularly well. That was some time ago. I was fairly against it when my DC were young and would n't have contemplated it for them. However having taken the difficult step that way, I think in the right school it is an amazing experience for a sociable child who likes trying things although undoubtedly difficult for parents.

I am very anti boarding. Too many children are damaged by it. I would keep her at home if you can particularly as you say it could be a London school. I really would recommend North London Collegiate. We felt no pressure there at all although most girls cannot pass the test to get in so it will be for children who will not pass the test.

Most Catholic boarding schools have not enough pupils and poor exam results. Eg if you have a bright boy he would be much better at Eton which has Catholic chaplain (if you think boarding okay - I don't) than at say Amp.

Thoroughly recommend Ashford School in Kent for day and boarding; just 35min from St Pancras. Both DDs loved it.

Sunshinequack my impression of at least some very academic schools is that the children exert pressure on each other and the staff try to counterbalance it. IMO bright children need a critical mass of other bright pupils to spark off as well of course capacity to teach them to their ability. Not all mixed schools have that.
There are some 'hothouse' schools where the staff only praise pupils for very high level achievements and I would definitely avoid those for a child (most I think) who need more positive reinforcement especially for boarding.
For boarding, Benenden gets good reviews as a non hothouse girls's school at the moment although may be too far south for you? St Mary's Ascot is Catholic girls' but I don't know anything about it.
King's Cantebury again seems well thought of by posters on other threads

Worth seems to fit your requirements. Benedictine school - not unlike Ampleforth. Close to London. Does well by all types of student. Not tremendously pressured.

Royal Russell is an interesting mix as single sex houses where tutor group takes place but co ed classes. Pastoral care is very good ( I think because of the small single sex tutor groups and house mistress ) It is small enough to have individual care but large enough to have all music, drama, design tech , art that you would expect.
My DD had come from a high pressured prep which was not right for her and she has really flourished at RR and I am confident she will now be able to perform to the best of her academic potential as she is happy and settled. A good range of extra curricular activities as well. Some people don't think it is academic enough though.

For nice but non- selective schools in the SE London area you could consider Emanuel or Royal Russell. Both coed, both good pastorally.