When it comes time to tote books and homework to and from school, might more children be using urban-style messenger bags than the sturdy stalwart backpack this year?

Toward the end of last school year, 8-year-old Anita Baume, the daughter of Teen Vogue fashion market director Gloria Baume, traded a backpack her mom had given her for a beat-up messenger bag.

Gloria Baume really thought she had picked a "cool" backpack, but she says that with her readers, too, backpacks are "done."

That's not necessarily good news for students' backs, says Dr. Mary Ann Wilmarth, director of the doctor of physical therapy program at Northeastern University's School of Professional and Continuing Studies.

"You want any weight you are carrying close to your torso or trunk," Wilmarth says. "If you have a significant amount of weight in a bag, a good backpack is better because it centralizes it. A messenger bag is lopsided."

The stress of carrying a too-heavy bag can cause muscle pain in kids' backs or necks, or, in children already with slight scoliosis, there can be an increase in the spine's curvature, Wilmarth says.

The best backpacks are those more likely used for camping — they have a frame and rests on the hips. Short of that, choose one that's not too big and has a waistband and padded shoulders, says Wilmarth, also a spokeswoman for the American Physical Therapy Association. "You want a backpack that doesn't allow too much to fit in it because, if you have room, you'll fill it."

But even Wilmarth acknowledges the style appeal of the messenger bag. Her tip: At least wear it diagonally across the body to help distribute the weight, instead of over the shoulder like a laptop bag or purse.

"Backpacks and messenger bags are both growing in total bag business — it goes with the move toward a generally casual style," says Tim Schifter, founder of Schifter + Partners, which makes bags for designer Jill Stuart and Gwen Stefani's L.A.M.B and Harajuku Lovers collections.

Back in his school days, Schifter, now the father of a 12-year-old girl, carried an orange nylon backpack. "It was cool to have a beat-up backpack with ink stains."

Stefani herself is hedging her bets. "I'm more into the messenger bag at the moment," she says. "I used to be a backpack girl — I carried one forever — and will always think backpacks are cool."

Beyonce, singer, actress and co-founder of fashion label House of Dereon, says, "Messenger bag, for sure. Messenger bag, all the way. It's like a big purse, not a big bookloader."