@Girlyy
Glad you found the right school for your DD. Re: class sizes though, I thought Croydon High , aimed for max 20 in reception, the same as Old Palace. At Old Palace they split the class if it goes over, for all years,
The differences are small between the two schools and it goes down to gut feel.
@Gigisaffron
Old Palace came 3rd for A levels behind Whitgift and Trinity for all schools in the borough of Croydon, so they're doing well academically. I think you'll always get people nitpicking with selective schools, I've seen no evidence of standards slipping, the opposite, it can be a little stuffy, grammar school-ish with the strict adherance to uniform and the competition between the houses.
The senior school is in town but right next to tram stations and train stations, the school bus also picks up and drops off all over London and South East on all different routes. Also a good few parents drop off their daughters at 7.30 for breakfast club and there's so many after school clubs and activities, even in preschool, pick is often after 4pm, with many not picking up till after work at 6pm, afterschool club has lots of girls, they get tea to tide them over.
Picking up at the Prep by car, is v.easy
The school's main playing fields are at the prep, but the senior school has the heated pool, netball pitches and sport hall, so it depends on the sport if the girls are on the bus. Girls also have access to the superb facilites of Whitgift Sports Club facilities and Trinity’s all-weather hockey pitches. The prep, Whitgift club and Trinity are all a 10-15 min drive away.
I think you need to take the school tours and go with your gut, bottom line a girl starting at Cumnor , Croydon High or Old Palace, none of them are wrong choices, they'll all be fine. You just look for the best fit for your girl, what you feel and what your DD feels and of course if she's offered a place following assessment, which is an un-exact science