WEST PALM BEACH, Fla. » Ah, late August — that most beautiful time of the year for parents: School is back in session.

Emphasis on the word "back."

From elementary through high school, kids now typically lug oversize backpacks weighed down with textbooks, laptops and other supplies.

And likewise, the risk for both short- and long-term spinal conditions spans from grades one through 12 — albeit for sometimes varying reasons.

Take pre-adolescent and/or undersize students. Their diminutive stature means that whatever load they’re carrying is a greater — and potentially more injurious — percentage of their total body weight than bigger kids.

Older, more physically mature students may be tempted to carry ever-increasing loads. And even if they’re not, the cumulative effect of years of carrying overstuffed backpacks is nearly unavoidable.

The American Chiropractic Association says that backpacks "should weigh no more than 5 to 10 percent" of a student’s body weight (ideally 5 pounds or less for a 100-pound child).

Of course, students worldwide rarely adhere to these kinds of recommendations.

As far back as 1999, Italian researchers found that "34.8 percent of Italian schoolchildren carry more than 30 percent of their body weight at least once a week, exceeding limits proposed for adults."

A more recent Italian study, says the ACA, found that children typically carry backpacks that weigh the equivalent "of a 39-pound burden for a 176-pound man, or a 29-pound load for a 132-pound woman."

And even when students can keep their backpack/body weight ratios to the recommended 10 percent or lower percentages, The New York Times noted: "The federal Consumer Product Safety Commission calculated that carrying a 12-pound backpack to and from school and lifting it 10 times a day for an entire school year puts a cumulative load on youngsters’ bodies of 21,600 pounds — the equivalent of six mid-sized cars."

No wonder, then, that a 2006 study conducted by the National Institute of Health concluded that "the incidence of back pain in early adolescence approaches that seen in adults."

So what can concerned parents do?

First, be sure that the backpack fits properly.

This means that it should hang no lower than 4 inches below the waistline.

According to Palm Beach Gardens, Fla., neurosurgeon Dr. Charles Theofilos, "Most youths, when carrying a backpack, hump their shoulders forward, which can cause pain between the shoulder blades."

In more severe cases, it can lead to scoliosis.

Theofilos recommends that parents "look for ergonomically designed backpacks that are lightweight and have wide, adjustable, padded shoulder straps." He also suggests having your child use hip straps and/or waist belts to better distribute the weight (although most kids resist doing this).

Another tip: Don’t buy a bigger backpack than what your child needs. The more space he or she has, the more tempted he or she will be to fill it.

And try to keep daily track of what’s inside your child’s backpack. Regularly clearing out unnecessary items is the best way to ensure that the load remains bearable.

Steve Dorfman, New York Times