I do know someone who sent all their kids to fancy private schools till the age of 18, with the proviso that when they wanted to go to university, they had to fund it themselves.
I had a mate who went through something similar – no agreement but his parents didn't support him at all in Uni and he figured that having to work in term-time wasn't ideal and they could have helped a bit more. Given that he's doing well now maybe they could have loaned him the money.
I worked in my holidays but never in term-time and had no support from my parents – that was in the last of the good times as we moved into the 90s.