@BenjiMcSchmenzie I was, carefully, suggesting an polite email every month or so to reconfirm interest. That is hardly badgering. I was specifically suggesting that demand for girls and boys might be different, hence why one might get a place, and the other not.
And I was suggesting be nice and respect the professional judgement that has been made. I did enough observing to postulate that schools like constructive and supportive, but not demanding, parents. And as they drill down the wait list the obvious differences in ability are tiny. So other factors come into play.
My understanding is that a lot on the wait list will lose interest. Either because they get offered a state school place or because they have paid a deposit and are liable for a terms fees at another school.
There is an issue for admissions officers. First I am not convinced that a wait list is in strict order. Schools want a balance of those with different aptitudes, including extra curricular. But as they get closer to the start of the academic year, and particularly into the summer holidays, they become more interested in those who are likely to accept the place. Rather than offer to the next on the list with a high probability that they will sit on it for two weeks then reject.
Do tell me if I am wrong.
FWIW, dd got through a Westminster sixth form wait list, for STEM subjects, which was unusual. These subjects were in demand and there would have been a lot of good applicants on the wait list. So a careful email explaining that this was the only sixth form she had applied to, and that she would certainly accept if offered as the school was within walking distance, and her brother had been very happy there so perfect. Otherwise she would stay where she was. And hey presto…a place.