Both my sister and I boarded from age 12. She loved it and made life long friends. I hated it! The fact the people who disliked, ignored and bullied me during school time were also the people who I was forced to live with after school made my life hell. I couldn't escape them. 24/7 with the same people. I was a slightly anxious, quirky child. I had a target of being different on my back they seem to see and if you don't fit in you are most definitely pushed out. I left an extremely anxious adult at 18 who tried to suppress my personality for fear of being ostracized further. Took me decades to like myself again.
Everything you read in Mallory Towers (which I had loved as a series) is bollock. Midnight feast are not a regular thing and not being invited to them when they were was painful. There is no sense of sisterhood and community. If they bully you at school, they bully you in dorms, at after school activities, at breakfast and dinner.
While I understand my parents reasoning behind sending me (also had an unwell mother), it alienated me from my family. I felt abandoned and never quite loved enough. I told them from term 1 it was hell, but I was still there 6 years later.
They didn't (and probably still don't at 52) see me as an adult as they weren't around to negotiate me changing from child to teen to adult. I was not a weekly boarder, only went 'home' once or twice a term, so that may be different for weekly boarders. My father particularly couldn't deal with his 'little girl' becoming a stroppy teen as it happened in huge leaps as we saw each other so rarely.
All the things I hated, were the things my sister love, she was a conformist, I was not. It was like banging a square peg into a round hole for me. And it damaged my shape for many years. Some personalities suit boarding, some really really do not.
I would really really only consider sending a child if they had the right personality and were removed asap if they don't like it.
Wow, that was cathartic!