My big sis went to local comp. She was very keen to go, but was very unhappy in later years there.
I got assisted place to local private school so went there (my sis refused to sit exam).
My little bro boarded at private school cos of divorce/family issues.
I was happy enough at school, and whilst lazy did enough (was forced to do enough) to go on to university etc.
After initial period db was happy boarding. It was a good school and gave him some much needed stability at the time.
Big sis definitely has a chip on shoulder about the whole thing. She doesn't feel she fulfilled potential or had opportunities I did. (Which is true)
However, I think this is largely due to the fact the comp. she did go to was a crap one (we were in middle of nowhere so there really was no choice). Effectively she was bullied for being bright and reasonably hardworking. This was then not helped by fact school was not set-up to cope with brighter/more academic pupils - so for example she couldn't do French, Geography and Biology O levels - If she did Geog and Bio they could only fit Childcare, Metalwork or Technical Drawing in not french.....
So,yes it did cause her problems but I think if she had gone to a good state school this wouldn't be the case.