@Everydaydayisaschoolday
I see this line about spoon feeding at private schools quite regularly and I have to say it is completely contrary to my experience (though it sounds like your son has done extremely well).
Good selective independent schools don't spoon-feed for exams. Because they are independent and have small class sizes, they have the option to teach way outside of the exam syllabus and to let children explore their own interests to a greater extent. At the prep school I am sending my son to they spend 30 mins a day from age 6 on their own interest - so if they like art a small group of them do an extended project of their choice with the art teacher or some of them each build a robot controlled by a computer etc. They have autonomy over what they choose to do and can change over time - the idea is to let them develop their interests in a semi-autonomous way from very early.
At my independent school for coursework we generally had the option to choose and plan our own project. So for English we chose our own texts, even if no one else in the class was studying them and for geography we planned and carried out our own field study rather than doing this as a group. My friends doing the same course at state school were given one text for the class and "taught" it or required all to go on the same trip and then use the same results. There were lots of personal projects throughout my time at school e.g. you had to do a debating competition on a topic of your choice.
If you wanted to study a subject which the school didn't offer at sixth form level they would try to offer it or find another school which offered it.
If a student wanted to enter a maths competition or set up a chess club etc. they would have support to do that but be encouraged to do a lot of the work in setting it up themselves.
I felt that at my school passing exams with As was the bare minimum and education was about much more than that.
There may well be private schools which are purely exam factories but I think it's an unfair generalisation and I personally wouldn't pay for a school like that.
If you had a bright child at a state school and they essentially have to teach themself with no support if they want to progress beyond what the school is teaching, I can see that that might really develop independent thinking but not many students are going to do that.