This is obviously a complex issue, dependent on the child's age, maturity, home situation, school, level of boarding and many more contributory factors
An anecdote from my own experience as a border from the age of 8 at a single sex Catholic school:
At the age of 15 I was a monitor. I remember punishing a younger child for some minor infraction by making him give me the letters his mother sent him: full of stories of everyday life at home. I read them for the sense of love and security that they gave me, even though that love was not directed at me. He told his mother and she said (he told me) how sad she was for me. It makes me weep even now to remember it - for my invasion of his privacy, for the lack of love in my life and for her understanding, at such distance, for a child she'd never met, for the shame I felt at the time at displaying such weakness and vulnerability
Aside from the very common tales of bullying, and sexual abuse, and of children crying themselves to sleep at night, the damage caused, to this day, to my self-esteem, to my ability to be emotionally open, to have proper honest relationships with people is incalculable.
People who know me see me as confident and polished. But I learnt at school how to hide my true self and project an image; it's almost a form of schizophrenia. I have, in almost every relationship I have had, had a secret life, led for the most part (but not totally) in my head. Because school was relentless; every thing I liked, every thing I disliked, was a weakness to be exploited by other pupils and so had to be hidden. Every success and every failure had to be met with a studied indifference, every fear hidden, every bit of joy or sorrow concealed.
Send my children to boarding school? I would rather chew off my own arm. Both for the damage it might do to them and for the joy that I would miss while they were away and later from their disconnection from me
Others will have had different experiences