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New York • A lost hoodie here, a forgotten backpack there. In Justin Bieber's case, an open fly on the Grammy red carpet!

What's with teens and brain fog?

Parenting teens and tweens can sometimes feel like kindergarten redux, except adolescent attitudes are edgier and their missing and broken stuff costs more. In addition, their table manners are atrocious, some don't like to shower or use deodorant, and they may forget to brush their teeth.

And while nobody would ever suggest that 16-year-old Bieber's grooming is anything less than impeccable (including his famously perfect hair), he experienced a classic, albeit minor, teen wardrobe malfunction Sunday as he posed for pictures in his all-white tux.

There was no reveal. His trousers covered all, but it was one of those moments that sets parents thinking: Why is my kid still skipping through life on another planet? When's he going to land back on Earth?

The short answer might be later rather than sooner, at least when it comes to their brains.

Most scientists once believed the human brain reached full development by age 12. But research based on improved brain scan technology indicates that coordination of certain functions continues to come together through the early 20s, said Lawrence Steinberg, a psychology professor at Temple University.

"It's not that a teen is forgetting," he said. "It's more like they're much more drawn to the immediate reward of a situation than adults are and they're much less likely to think ahead and think about the future. The future can be just an hour later."

Steinberg regularly hears from parents as the author of the recently revised You and Your Adolescent: The Essential Guide for Ages 10-25.

"These days I get almost as many questions from parents about dealing with 20-somethings as I do about teenagers," he said.

Aimee Stern in Silver Spring, Md., is dealing with a full-on black hole fed by her 11-year-old daughter and 15-year-old son. "We've had multiple lost cell phones, house keys, winter coats," she said. Does she think mom and dad are a match for the scattered adolescent brain? Stern relaxed after digging into the latest research herself as part of her work writing a guide about teens and alcohol use.

"It was such a relief to learn that I wasn't crazy, and my kids' forgetfulness was just a normal part of brain development," Stern said.

Brain fog is a life force at the Waterville, Maine, house of Marc Pitman. He has a simple, standing request for his 11-year-old son: Shut your bedroom door. "He'll go to close the door, forget on the way and come back to the living room having left his door open."

Pitman relies on "auctioneer-like repetition" of common-sense instructions.