School policies that let parents know when their children are overweight or obese appear to have little impact on the problem, a new study finds.

In the last decade, almost all public schools in California collected information about height and weight on kids in the fifth, seventh, and ninth grades, but only some opted to send the results to parents. This gave Dr. Kristine A. Madsen of the University of California, San Francisco, a unique opportunity to evaluate the impact of that notification.

She found that children whose parents were told they were overweight were no more likely to have lost weight years later than children whose parents were not notified.

These findings, reported in the Archives of Pediatric & Adolescent Medicine, suggest that school officials should concentrate their efforts on interventions that have the most impact, such as making school lunches healthier, and increasing the use of physical activity, Madsen noted.

"Physical education is probably the most underused public health tool we have," she said in an interview. "We really would urge schools to make sure their environments are supporting physical activity to the extent possible."

And letting parents know their kids have reached an unhealthy weight could still have an impact, Madsen said -- most parents were notified via letter, which some may not have received. Plus, almost none of the letters used the terms "overweight" or "obese," instead referred to kids' "body mass index," a measure of weight relative to height, which some parents may not understand, she added.

"Even if they see the letter, we think they may not get the message."

Health experts are currently divided over the benefits of schools screening kids for BMI -- currently, the Institute of Medicine recommends it, along with parental notification, but other agencies such as the Centers for Disease Control and Prevention and the American Heart Association maintain there is not enough evidence to support the practice.

The nation's schools reflect that division: As of 2006, 41 percent of school districts required officials to measure kids' height and weight, and three-quarters of those schools notified parents of the results.

That the current system is not having an effect is not a huge surprise, Madsen told Reuters Health.

Even if parents modify the home environment by providing healthier meals, for instance, if nothing changes at school -- where kids spend most of their time -- it's going to be hard to see an effect, she noted.

Plus, a single letter may not be enough to convince parents to make drastic changes at home, since they often have other issues they are dealing with, she added. "Most parents are already doing the best that they can."