How much sleep do teenagers really need and why do they feel the urge to stay up so late? Teenagers need more sleep than adults and their circadian rhythms are actually different, says parenting expert Nathan Wallis. On average, a teenager's body clock moves forward around two hours so, effectively, we can think of Kiwi teens as operating on Sydney time - "they're two to three hours out from the rest of us." He gives parents some tips.

How much sleep do teenagers really need and why do they feel the urge to stay up so late?

Teenagers need more sleep than adults and their circadian rhythms are actually different, says parenting expert Nathan Wallis.

On average, a teenager's body clock moves forward around two hours so, effectively, we can think of Kiwi teens as operating on Sydney time - "they're two to three hours out from the rest of us."

Wallis gives a couple of examples of how different hormone levels affect teenage body clocks.

"If your kid used to have enough melatonin to fall asleep at 11pm - they don't have that same amount until 1am.

"If they don't have enough cortisol to wake them up in the morning at 730am - they don't have that same amount until 9:30am."

As a result, teenagers aren't the most receptive to learning first thing in the morning, and often more wakeful and productive when they're heading home from school between 3pm and 5pm, he says.

Some schools overseas start the school day later.

In New Zealand, Wellington High School did a trial in which students could choose an 11-to-5 school day instead of a 9-to-3 school day and had some good results, Wallis says.

In general, teenagers need more sleep than adults, so don't worry that your teen sleeping more is a sign they're dropping out of life.

"How you're sleeping as a teenager has no relation to your work ethic as an adult."

Is "catching up on sleep" in the weekend effective?

Research says this won't work long-term, but you could conceivably "catch up on sleep" you've missed in the second half of the week on a Sunday, Wallis says.

If your teenager seems to be repeatedly hiding out in their bedroom as an escape from people and/or life, this could be a sign of depression so investigate that, he says.

Teenagers usually aren't able to manage their own circadian rhythms, Wallis says, and those with bedtimes regulated by their parents generally do better.

Explaining to them why they need to get sleep and nagging them to go to sleep won't be effective - instead, focus on helping them wind down in the evenings so they'll have enough energy to get up for school the next day, he says…

Go to this episode on rnz.co.nz for more details