I work in a boarding school, being a from a comp school background myself.
My job means my daughter will get a place in future, so I have given this substantial thought. I think I can give a fairly balanced view on this for anyone thinking about boarding.
I have worked with with some excellent boarding staff. Also, my experience in education in general is that teachers and schools care about the children, with few exceptions. Generally though, parents love them in a way that schools can't replicate. I have also seen girls struggling with friendships suffer from boarding.
That said, I have taught pupils who experience 'affluent neglect', and would be left to their own devices in a mansion with a housekeeper, so for those pupils boarding school is far more nurturing. Other than that, I disagree with full termly boarding.
Young people who are quite social and well adjusted can thrive in flexi boarding models - 1-3 nights a week in boarding - and I would say that's the best way to experience it and the confidence it can bring.
I would advise against any more than 2 nights boarding for children under the age of 13, and I would always choose a school where boarding is optional. This means you can wait for your child to request boarding, and you have the choice to make them day pupils if they're unhappy in boarding.
Boarding all term, or even all week, from under 13 is handing over parenting to an institution, in my opinion.