Driving on public roads in order to train a new student driver is the best way to go. Once a young driver has the theory basics down, it's time to get out there and experience the real world. The horns, the bikes, the angry drivers. All while having an experienced driver in the car to mentor them. They will eventually learn all the proper methods to be a skilled, considerate and safe driver. All in due time they will learn to be an arrogant, inconsiderate angry driver like the rest of us.
It is not, however, necessary to learn to parallel park on the road.
These are public roads. Not your personal practice grounds. Am I the first one to think of this or has someone else in the world realized that parallel parking can be simulated in a parking lot? Don't get me wrong. Parallel parking is a must for new drivers (and wouldn't hurt as a refresher for old drivers). But really, why on the road?