I just ask this: do you think that a qualified and experienced maths/English/science teacher who knows the curriculum is going to do a better job at teaching your child those subjects than you would?
Most people would agree that, yes, they are much better at that task than they (the parents) would be.
Then my second question would be: what on earth makes you think that those same people, or their colleagues, are going to do a better job of effectively parenting your child?
Even if you do believe that, you most probably haven't even interviewed or chosen which teachers/staff will parent them better than you - you just assume that any of them will do, without even knowing who they are.
If you knew an excellent plumber and got her in to do all of your pipe repairs and heating work - which she does indeed do admirably... would you ask her to choose your next car for you or arrange your re-mortgage, just assuming that she'd be better at it and more knowledgeable than you would be?
If not, what's the difference - apart from that your child should be far more precious to you than a car or a financial product?
I'd love to know why parents choose boarding school, because to my mind - in most cases (with exceptions such as for children with very specialised needs) - there are only two reasons: either you don't reckon you're any kind of basically adequate parent or you just prefer living the majority of your life without your kids in it. Neither of those make you look good; and if it were parents from deprived communities rather than wealthy, privileged parents admitting that, I think things would play out very differently indeed.
After all, which is better: constantly shouting and swearing at your kids because you can't be bothered with paying them attention or doing standard parenting things for them; or just sending them away and paying somebody else to do it all, so you never need to even think about bothering to regularly tell them to f-off?
I think it's extremely telling (and deeply sad) when a child would prefer to live with and be brought up by a random bunch of professional strangers who don't love them but are only doing it because they are paid to, rather than their own parents, And if they don't prefer that, how extremely cruel is it to send them away from you anyway?
Why on earth would any parent actively choose not to have a normal, close, loving, active parent-child relationship with their son or daughter when they are still young? It flies in the face of all of the most natural instincts that a parent should have.