here
I don't know about this.
I left school at 16 (about a month before my 17 birthday) with four good highers and a place at uni. I wanted to work and save money for a year.
My brother - very dyslexic (not that I am excusing him) - never did well at school, almost expelled from one, expelled from another, never went back, has no qualifications and is currently, well, he had a job selling the Daily Record last time I saw him, but, well, I don't know how long it will last.
Anyway, being made to stay at school til 18 would never have helped me, I doubt it would have helped my brother, stay on to get expelled agained? (With a load of other trouble makers?!)
But, OTOH, I guess there are some people who it would help raise their aspirations, and improve their opportunities...?