In all likelihood, both children had the same needs. It's just that Sheila -maybe because she was female?- knew how to get her needs met. Why did not JB "kick off"? Probably for the same reasons my friend's son didn't, although he has opened up since. I suspect that it takes rather more than boarding school for someone to want to commit murder, but it could certainly contribute to a very long list of things which might.
To be perfectly honest I think Jeremy had been scared of his own shadow whilst growing up as such an upbringing can either kill or cure depending on the type of person one is. It didn't do Sheila any good as getting pregnant was her way of escaping then things went from bad to worse.
Any parent can tell if their offspring is a bright scholar or not or if they're of the mindset to be sent away to boarding school. Invariably it's the parents decision and not the child's, whether because both parents work or because it's convenient to do so, I personally don't believe in it because separation isn't good to start with and never having been separated from my own parents I can't begin to imagine what effect it had on a child, but it certainly would be everlasting.
My dear pa-in-law had my daughters lives mapped out as soon as they were out of nappies by offering to send them to the local Montessori school. I was horrified at the time to think that they'd be taken from 2 years old, so I declined. Even when it was suggested they go to a private school after primary age I politely refused. Initially because their half brother and sister were never offered the same when they'd been young as it didn't seem right to me even though they were years apart age-wise.