With teaching any subject it's not ideal to adopt a 'one size fits all' approach. Some people learn quicker than others. We all know someone who passed first time after a few lessons; and someone who hasn't got a hope in hell, no matter how long they try. 'Accidents' on the road have many different causes.
No matter how difficult you make it to pass the test, you will never change the 'attitude' of some drivers. You might make them a bit more technically competent, or more aware of their responsibilities behind the wheel; but how do you remove the influences of teenage hormones, peer pressure, bravado, natural aggression, sheer stupidity, drink & drugs etc, etc ?
There already is compulsory retesting after certain offences. Whether the net needs to be widened is another debate entirely. Compulsory retesting after getting a parking ticket, anyone?