The difference amounts to how much time they have to waste. I didn't care about grades 'till grade 12. From 9 to 11 my grades hovered around 65% to 75%. I didn't do any homework, besides the obviously mandatory huge projects/group work. As soon as Grade 12 hit and the universities were watching I studied every night and got mid 90s. Best decision I ever made. I learned VB & SQL during that time, some electronics, so mechanics, worked as a programmer found out I hated it. All vastly more useful than a 92% in grade 9 drama or art.