FRIDAY, Aug. 26 (HealthDay News) -- Saying "no" to the school bus and walking kids to school instead could be a step -- or more -- toward boosting children's activity levels, a new study shows.

Texas researchers split a group of 149 fourth-graders from eight schools in Houston into active commuters -- those who walked to and from school up to five days a week -- and a control group who were driven by bus or car. At the beginning of the study, both groups had logged similar amounts of moderate to vigorous activity, about 46 to 49 minutes per day.

But over the next five weeks, the kids who walked to school upped their activity slightly -- an average of 7 extra minutes per day of moderate to vigorous exercise. In contrast, those who got driven to school actually lowered their daily activity over the study period, to an average of 41 minutes daily.

While the activity increase for walkers may seem modest, study author Dr. Jason Mendoza said that even small amounts of exercise are meaningful in a country with a 17 percent obesity rate for kids under age 19. About a third of adult Americans are obese, and another third are classified as overweight.

"It's not like they're going to the gym to work out," said Mendoza, an assistant professor of pediatrics at Baylor College of Medicine in Houston. "It's something they can build into their days without a lot of extra effort or equipment."

The study is published in the September issue of the journal Pediatrics.

Because of a "car-centric" society that favors wider roads and fewer sidewalks -- as well as a heightened fear of abductions by strangers -- far fewer kids walk to school than was the case four decades ago. According to study authors, 42 percent of children actively commuted (walked or biked) to school in 1969-70, compared to only 13 percent in 2009.

Because of the brevity of the study period, Mendoza's team did not compare differences in the children's body mass indexes (BMIs) over that time, so it's impossible to say that the intervention caused the kids to lose (or at least not gain) excess weight. But all participants came from low-income districts with high numbers of ethnic minorities, groups that tend to have higher levels of childhood obesity.

Study staff members took the helm of "walking school bus" groups of up to a dozen kids or more, Mendoza said, some of whom were also accompanied by parents who wanted to participate in the effort.

Programs like this are supported by the Safe Routes to School National Partnership, a national organization that advocates for safe walking and bicycling to and from schools.

However, walking school bus programs are still not exceptionally common, said Dr. Silva Arslanian, chief of the weight management and wellness center at Children's Hospital of Pittsburgh.

"The results aren't surprising," she said. "The real question is what happens once you stop the activity. The important thing is to sustain a behavior, and that's always been the difficulty in obesity prevention or treatments programs."

Arslanian wasn't impressed by the fact that only 26 percent of the families who were approached for the walking school bus study decided to participate.

"A 75 percent refusal for any study is extremely high. So, are people averse to the idea of walking?" she said. "Parents are not interested because they themselves are heavy, or have other burdens. It all boils down to role modeling and expectations in your child."

Of course, walking to school versus being driven does require a bit more time -- the study showed a 38 percent jump in relative commuting time between the two groups. But Mendoza believes that parents can make "walking school bus" programs feasible by approaching them as a community endeavor.

"Usually walking school buses split up days, like carpools, so it should save parents time if they get other parents to help," he explained. "There are parents who've decided to leave the car at home and take turns walking the kids to school. It might take a little longer to do it, but they build it into their day. It's good for them and good for the kids."

Another advantage of the program is decreased traffic congestion around schools, where carpool lines can pose dangerous circumstances for kids getting into or out of cars, Mendoza noted.

"I'm hoping policy makers and public health officials consider supporting these programs," he said. "It's a broad-based way to get our children to be more physically active. We could say it's an old-fashioned idea, but what's old is new again. We're adapting it to the reality of today."

The Safe Routes to School National Partnership has more information about walk-to-school programs at www.saferoutespartnership.org/about.

More information

Find out more about walk-to-school programs at the Safe Routes to School National Partnership.