Here are the warning signs.

More details are emerging about the boy who committed suicide yesterday at The Dalton School in NYC. Some students said Theodore (Teddy) Graubard had been noticeably depressed recently.

"He has been very depressed. People were talking about him having a breakdown last week," said one student, who asked not to be identified.

According to the World Health Organization:

• Depression is the second most common childhood mental health problem.
• One in 33 kids is depressed.
• The number of kids diagnosed with the disorder could double by the year 2020.

Scary, huh?

Even scarier is that less than a quarter of the 12 million kids in the United States who suffer from mental disorders receive treatment, which makes them more prone to lower grades, drug and alcohol abuse and criminal behavior. Kids with untreated depression are also 12 times more likely to commit suicide.

Many parents don't seek help because they fear their kids will be stamped with the "mentally ill" label, while other parents dismiss their child's behavior as a phase.

How can you tell the difference between a kid who's moody and one with a mental disorder?

We called Dr. Miriam Kaufman, the mother of two teenagers and the author of Overcoming Teen Depression, for guidance.

Dr. Kaufman says the signs of teen depression can be particularly confusing for parents, because depressed teens can display opposite symptoms. For instance, both increased and decreased appetite are signs of depression, as are not sleeping enough and sleeping too much. "Some depressed teens display signs of psychomotor retardation, and appear as if they're moving through molasses, while other kids seem jumpy and agitated," Dr. Kaufman continues. "Some depressed teens cry all the time, while many never cry at all."

Other signs of teen depression include:
• Lack of attention to personal hygiene
• A change in social behavior, such as not hanging out with friends as much (if at all)
• Decreasing grades at school
• Poor concentration
• Talking about death or suicide

"Parents should be on the lookout for a real constellation of these symptoms -- a lot of things going on at once -- that's lasted for a while," Dr. Kaufman advises (at least a few weeks).

If you notice your teenager slams doors and seems very upset around you, but then hear him laughing and being his usual self with his friends on the phone, he's probably okay, Dr. Kaufman says. "What you're looking for is overall behavorial changes at home, at school, and with friends, across the board," she adds.

If you suspect your teen is depressed, Dr. Kaufman says it's important to see your child's pediatrician or primary care physician. "A lot of other things could be causing the symptoms -- such as hyperthyroidism and substance abuse -- so you don't want to take him straight to a psychiatrist without looking at the whole picture and ruling those things out first," she concludes. If your child is suffering from depression, your primary care doctor will likely refer him to a psychologist, family counselor, or psychiatrist to provide the help he needs.

Our hearts go out to all those affected by the Dalton School tragedy. We hope that this will serve as a wake-up call to other mothers whose kids are battling depression. Cases like these are a terrifying reminder that depression kills.