That's a pretty stupid ruling if you ask me. If you can drive and pass whatever you need to pass then you should be able to drive. It should have nothing to do with how well (or not) you're doing in school.
Over here (in South Australia, each state has different road rules) as long as you pass you learners test (exam type thing on road rules, must get all give way questions right [6/6, 8/8, or 12/12, can't remember], then you have to get 28 or above out of 40 on the rest of the other questions to pass), drive supervised with a fully licensed driver for 6 or so months, go for your P's (another test, driving in the car with a cop, if he passes you, you have you're P's and are allowed to drive by yourself). You have P's until you're 19. Then you are fully licensed.
Pretty sure that's right, although, they are the old rules, (year or so ago, maybe a little longer) they've changed them now. I was lucky I got my licence under the old rules. The new ones suck. And I can't remember what's changed.