In all schools class sizes will vary. Big name schools often have tiny classes for subjects few do, such as Greek or perhaps Music or less popular languages. Subjects such as Maths, the sciences, History, Economics will probably be larger. In the schools I have contact with, these subjects seem to vary from about 8 to about 12. When there are several classes in a year group, timetabling will often mean there’s at least one larger group and one smaller group and they will rarely be of equal size….so until September you probably cannot know for sure what class size you will have.
Personally, I like around 8 students…..it’s enough for discussion, without the marking load being too vast. Beyond 12 and the marking load is getting big, especially in essay subjects.
In all schools, some subjects are effectively cross-subsidising others. Many have small groups in languages whilst others are 3 or 4 times larger.
I wouldnt let it be the key factor in choosing. Students quickly adapt to the class size and the teacher will teach with the group size in mind and adjust activities. There are pros and cons of small and larger classes. Often state schools will go above 20 for A Level….that kind of size impacts the kind of teaching that can be done….a bit more like a GCSE class rather than a seminar style. But of course, lots of students get great grades and in the end you have to have what’s available at your school.
Students leaving year 11 can be horrified at the thought of a class of 5 and think it will be too intense with nowhere to hide. Nowhere to hide isn’t a bad thing, and again, it’s just something most aren’t used to from earlier on. They quickly adapt and even being in small class for one subject and bigger for others, all can feel normal as they just accept what they find themselves in and the expectations and style of different teachers which can be quite different, regardless of class size.