Marks don't prove shit, but as you'll need high marks, I suggest you cheat.
They do prove a bit more than just 'academic excellence', contrary to what most people think. I think that high marks first and foremost prove high competency and dedication of a student to the responsibilities/tasks he's given. It's something that goes on through the course of life and if you start screwing it up in high school, it's very likely that you'll have even bigger difficulties coping up with responsibilities after high school.. just putting this out from personal experience.