@Nutmegger the UK is weird in that it has an (ethically dubious) two-tiered education system. Most of the schools in the country are non selective and take in children based on distance and siblings. But a significant number of schools take in students based on academic tests and interviews. Most of these are also fee paying private schools.
These selective schools are incredibly competitive - with the most selective schools often having over 2000 applicants for fewer than 200 spaces.
Today is the day when the majority of fee paying schools release offers to their candidates. Many children who have not received an offer will be put on a waiting list (WL). A WL place will often turn into an offer as other children reject schools in favour of other schools.
The other UK oddity is that we do run this process quite young. The majority of kids mentioned in this thread will be 10 years old.