As per some of the other comments on this thread: there are some badly out-dated views of Claremont Fan Count being expressed (they were out-dated even in 2022!).
It took <10mins of research to confirm that the "new" headmaster started in 2018: Will Brierly was the former deputy headmaster and head of academics at KCS Wimbledon (#12 in the country).
Search for interviews with him or his own social media posts: he's regularly stated that he is NOT trying to recreate KCS's academic culture, but the school has been slightly more selective that it has in the past, but he wants parents to focus on "value added".
With that in mind, I'm not sure how much more selective they are being, but the results are already showing: they're a fair way behind some other schools in the area (Kingston Grammar / Surbiton Girls), but they already have GCSE rates ahead of St George's Weybridge!
A-Levels students would have started around the same time that he did, so the scores are probably reflective of a less selective approach 6 years ago.
My kids are a long way from A-Levels, so I'm fine with placing more weight on the GCSE results.
Exam results 2023 (Claremont Fan Court)
A Level A & A* grades
39.69%
GCSE level A & A grades*
55.00%
https://www.best-schools.co.uk/schools/1331/claremont-fan-court-school-esher
Exam results 2023 (St George's College Weybridge)
A Level A & A* grades
54.00%
GCSE level A & A grades*
50.20%
https://www.best-schools.co.uk/schools/2330/st-george-s-college-weybridge
St Johns don't post their GCSE results, but their A-Level results are between Claremont Fan Court and St George's:
https://www.best-schools.co.uk/schools/2363/st-john-s-school-leatherhead
The more recent, younger academic scores are backed up by the more anecdotal "evidence" I gather is no longer the shoe-in it used to be!