Do private prep schools really lead to better outcomes compared to state primary schools?

I’ve been reading a lot about the UK education system and how private prep schools are often considered a gateway to top secondary schools and universities. Many parents seem willing to pay a lot for these schools, believing they give their kids an edge in life.

But does attending a private prep school truly lead to better outcomes compared to state schools? Is it the smaller class sizes, better facilities, or the connections that make the difference? Or could a bright, motivated child achieve just as much in a good state school?

And if you’re a middle-class family, is the “advantage” of private prep school really worth the financial sacrifice?

I’d love to hear from anyone with experience in either type of school—parents, teachers, or former students. What are the tangible differences you’ve noticed, and do you think the private prep school “advantage” is worth it?

Edit: For context, my child is working at “greater depth” (GD) level in his current state primary school and the teachers says he is advanced for his age and among his classmates. He loves learning and is very motivated. He loves his current school and has some great friends. We are a very supportive family. I am considering if it is worth moving to a prep school but worried about the costs.