I'm sure you've noticed that as soon as people are around a police car they suddenly "behave" - drive the speed limit, signal, hang up the cell phone - and just as quickly resume their bad habits once the police car is out of sight. People know how to drive, they just don't practice the good behavior unless the threat of getting a ticket is imminent. But if you start someone off driving in such a way that they're forced to use the good behaviors, more of those habits will stick.
The reason for my drastic suggestion is that the system doesn't work. New drivers get relatively little time with instructors, and in my experience many instructors are not that good of drivers, much less teachers. They then drive around with their parents, most of whom are also not very good drivers, and in most cases have been "teaching" bad habits for their child's entire upbringing. Driver's tests are what, 20 minutes long? There's no way to measure driving comprehension in 20 minutes (other than abject failure).