Katherine K. Dahlsgaard, lead psychologist at the Anxiety Behaviors Clinic at Children's Hospital of Philadelphia, wrote this for the "Healthy Kids" blog.

This happens all the time: A tearful teen sits before me, describing pretty crippling depression or anxiety, and sometimes both. We are in a session, I am her therapist, and I am nodding sympathetically.

Then I ask: "What time did you go to bed last night?"

I am alarmed by her answer, "like, maybe 1:30?"

I am even more horrified to learn that she typically clocks between five to seven hours of sleep a night, "maybe a little more" on weekends.

I tell her all about the dangers to a teen's developing mind of not getting enough sleep. I recount the grim statistics on crashes caused by drowsy driving. My sympathetic nodding is quickly replaced by finger-wagging.

(Moms and Dads, I'm not suggesting you try this at home. Therapy-through-nagging works about as well as parenting-through-nagging, especially on teenagers).

My method may be suspect, but my heart is in the right place.

Sleep deprivation is dangerous to a teen's mental health, according to a nicely designed study published last month in the journal Sleep. Researchers followed more than 3,000 Houston-area teens aged 11-17 for a year. Teens were interviewed for one to two hours about their mental health and sleep habits; they also filled out questionnaires. One year later, families were visited again and the same information was gathered.

The researchers found that sleep deprivation greatly increased teens' risk of developing depression over the course of the year they were followed.

So why is it that teens do not get enough sleep?

First, puberty shifts teens' internal circadian clocks, making them naturally become tired later. Teens have jobs and activities that keep them out late.

Then there's homework. Not to mention the siren calls of Facebook, texting, Kindling, Snapchatting, Instagramming, and the like that conspire to keep them up even later.

And the older you get, the earlier school starts.

How much sleep does the typical teen need? Nine to ten hours a night.

How much sleep does the typical teen get? A lot less than that - with about 20 percent of teens reporting they get fewer than 6 hours a night. (This statistic keeps me up at night.)

So what can parents do? Probably the same thing that I do with my sleep-deprived patients, once I've stopped lecturing:

Educate teens - with facts, not opinions - on how much sleep they really need to function well.

Help them problem-solve regarding how they can:

  1. Complete homework efficiently.
  2. Have a regular bedtime that they stick to no matter what.
  3. Police themselves to turn off all electronics once they settle down for the night.

Provide relentless cheerleading and support for the next few weeks as they test these changes, until they find out on their own just how good it feels to get enough sleep.