I'm completely OK with private parents deliberately changing sector to offset the discrimination some universities now apply against private school kids. Working around discrimination is justified..
And it does work. For Cambridge at least, whose preference for 'social injustice' over academic excellence is becoming ridiculous for a university which is supposed to be a UK leader.
www.telegraph.co.uk/news/2023/05/16/private-schools-university-entry-cambridge-state-schools
If you read the article, Cambridge say that applicants are not “gaming the system” because admissions tutors are aware of an applicant’s full education history...
Yet
"In 2022, the acceptance rate was 24 per cent for those who changed to sixth form college and 25 for those who switched to grammar. This was almost 33 per cent higher than the 19 per cent acceptance rate for private school children."
So it's really not surprising people make the switch, because it does work. Not because of contextualisation of schools with worse outcomes... but because of straight, deliberate discrimination against private.
On a similar vein, degree class awarded at Cambridge turns out to be significantly higher for students from private school than state, even after adjusting for factors such as grades at entry and income. Ie students from private get a better degree class than students from state with the same grades and the same family income. So much for a grade from private being worth less than the same grade from state! In reality, that grade from private leads to better ongoing achievement.
Which is exactly what you would expect following discrimination: those who do get in from private are much stronger and do better than those from state.
It's quite funny that when the results turned out that way for students from state school 40 years ago, it was seen as being the result of unfair barriers for state students... and Oxbridge went to huge efforts to widen participation... but then when the evidence clearly shows that they've swung too far the other way, then suddenly the same outcome means something totally different when it applies to children they don't like. 