Another PF parent here. Just add on setting, I think they take a very measured approach here. Note that languages are also in sets. So typically 3 form groups but then 4 sets for each subject where setting is relevant. In maths for my DDs year, there are 2 x top sets, 1 x middle and 1 x lower.
The other good thing is that just because you are in one set for one subject, it doesn't follow that you are the same level set for a different subject. So my dd is in top set for maths and science, the middle sets for languages and then the lower set for English. She's dyslexic. She gets 1 lesson of learning support a week - which you have to pay extra for.
Sport also features and so if your dds are sporty, you can kiss goodbye to Saturday morning lie-ins as there are fixtures most Saturdays and then if they are swimmers, runners, netballers and hockey players, you will probably end up having matches most week day evenings too.
Its been interesting to try and fit it all in - especially if you have other extra-curricular activities too. There are quite a few girls who are also members of local swimming clubs and also Guildford hockey club. Homework on top of all of this too.
Lots of drama clubs, music, etc. but I don't know as much about all of that as my dd is not interested in that side of things.