Once upon a time there was a young boy who nervously sat at the wheel of his mother's car while a driver's licence examiner sternly issued orders.

The boy did exactly as he was told, turning this way and that, following the examiner's instructions precisely. Happily, even though his parallel parking was less than perfect, the young boy passed his test, became the proud owner of an Ontario driver's licence, and drove happily ever after.

If only. In real life young drivers, aged 16 to 19 years, have the highest risk of being killed in a traffic collision.

In the real world, a teen driver is likely to fill her car with distracting friends (some without seat belts), crank up the music and speed on down the road while talking on a cellphone.

In the real world, driving is a complex task for everybody. But lack of experience, along with driver immaturity, less-developed vehicle control skills, poor hazard perception, peer influence and, yes, just plain reckless behaviour, has repeatedly proven to be a lethal combination for young motorists.

It seems, however, that teens shouldn't take that last bit about reckless behaviour personally, as a new study reports that the part of the teenage brain that inhibits risky behaviour simply isn't fully formed yet and apparently won't be until about age 25.

Pediatric psychiatrist Jay Giedd — who leads the ongoing U.S. National Institute of Health study, which utilizes magnetic resonance imaging of subjects' brains — describes teenagers' brains as being still under construction and not fully mature at 18, as was previously believed.

While more research is needed to better understand these findings and their implications in driving, American legislators are already citing the brain development research when proposing bills for new teen-driver restrictions.

Meanwhile, Ontario parents who lay down the law to teenagers about piling too many kids into the car will soon have legal statutes to back them up.

Though exact wording is yet to be confirmed, as of this September, G2 drivers 19 or under will be restricted to carrying only one 19-or-under passenger for the first six months, then up to three such passengers for the next six months, unless a G-licensed person with at least four years of driving experience accompanies them.

This in the wake of research that found that as the number of passengers increases in a car driven by a teen, so does the likelihood of fatal injury to that driver.

Such scientific studies, along with anecdotal evidence, common sense and personal experience, are what parents tend to rely on when faced with the difficult and often thankless job of establishing rules for their teen drivers.

So, about those cellphones. In the state of Maine, drivers with a learner's permit or intermediate licence are already banned from driving while using a cellphone, and many other states are poised to follow suit.

With no such laws in Canada (Newfoundland prohibits all drivers from using hand-held phones), it's left to parents to initiate their own ban, usually not a popular decision with cellphone-loving teens.

Parents could, however, tell their kids about a study recently published in the journal Human Factors, which found that talking on the cellphone made 18-to-25-year-old drivers react to brake lights from a car in front of them as slowly as 65-to-74-year olds who weren't using a cellphone.

Maybe the idea of acting "senior-like" will so repulse the young'uns that they'll put down the phones and drive attentively. Hey, you go with whatever works, right?