DD went to a selective private school for sixth form, having been educated in the state sector from reception onwards. Educated entirely in the state sector myself, it had never been part of the plan for DD to switch to an independent school, particularly as her comprehensive, like mine, was high performing.
All that changed when a careers adviser suggested to DD that she consider applying for a music scholarship at one of the two private schools in our city. She was successful, and reflected very thoughtfully on the taster lessons she attended as part of the application process, seeing immediately that pupils were more challenged and stretched. The school then (seven years ago) accepted girls only in the sixth form. It has around 700 pupils across two sites (pre-prep & prep, seniors) and a Christian ethos that is apparent in the day-to-day life of the school.
One of her chosen A level subjects was French, which she was to go on to study as an undergraduate. In preparation for GCSE, I spent time filling in gaps in grammar, which seemed to me substantial. Once she started the A level, she realised that those who had been at her new school all along had a firm underpinning to their knowledge of the language that was quite lacking in hers. At this stage, her written work was marred by basic errors.
For the first time, I understood why people pay: for more individual attention pedagogically and pastorally, freedom from performance tables, a broader range of extra curricula activities and trips, in-house catering producing a proper lunch, more congenial buildings, a variety of well tended outdoor spaces. I am very pleased DD had that experience for her final two years of school, and that she recognises what a privilege it was, particularly being in a class of two for French. My reservation is that an entirely private education is in most cases a sheltered education socially.
As to whether my daughter was happier at an independent school than at a state school, I can't say because she was never unhappy at school, with the exception of a bit of a tempestuous Y9.