Since you asked about good state school I'll reply as someone who can easily afford private but has chosen not to.
Firstly, yes, the class sizes are 30. I have no issue with this at all and when we looked at both state and private schools were put off classes of less than about 22. I think that the bigger classes give a far better opportunity for children to find their niche. In a good school such as ours which has a teacher and at least one assistant even in juniors this isn't a problem at all.
It's academically excellent and my very bright DS is constantly challenged and extended whilst the less able children are well supported.
There is far less testing than at the local private schools, no end of year exams and I'm happy for them to do SAT's. There are parents evenings every term and a report at the end of the year. Absolutely ample.
It has excellent pastoral care, great rapport with the local community and the children are happy, well behaved and confident. Discipline is high and I would say that given that many of the children have either older or younger siblings in private schools most parents feel the same.
My DS is working about 90% to the level of his peers in academic private schools. His handwriting isn't as good and his creative writing isn't as advanced but his other skills are very close and he's way ahead in maths. The schools offers plenty of afterschool opportunities and music.
What isn't as good? There's little emphasis on art and music and there's not enough sport but for primary level none of those are a deal breaker for me. My kids are happy, challenged, well adjusted and more importantly than anything for me, they're part of the local community, walk to school and have all their friends on the doorstep.
Like others we pick up what they miss out on at school with out of school activities which are full of private school children so they're obviously not getting everything from their schools.
Secondary is a different matter and I will probably send mine privately at 11 because of the extra curricular and broader timetable but for primary we've no regrets at all.
I do appreciate that we're probably not the norm and our school is mostly professional parents, DS's class off the top of my head has parents who are hospital consultants, Bankers, City Lawyers, Hedge Fund Managers, dentists, an actuary, Managing director of a public company, partners in management consultancy, and who were privately educated themselves and it's reflected in the way that the school had developed.