They're more interested in the comments not the marks- ie. attitude. I'll put it this way, if you're a good person at school (helping people, communicates well, focuses in class as opposed to distracting people) then that could translate into a good work ethic which a company/business wants- however if you're a jerk at school and piss everybody off...... well... But I'm sure you're not that =]
But you sure you've never done any work before? I put Young Achievers and yr10 work experience down on my resume, charity stuff comes under extra curricular but if work experience is empty I guess you could put it there too. I'd rather not put a heading in if it's empty- but whatever you do- don't lie. You can embellish but not lie.... but sigh, if you do choose to make something up; don't say you worked somewhere where you'd get paid because then they might wonder why you don't have your ex-boss/manager as a referee.