Any parent or teacher can tell you that schoolchildren tend to slip back a bit academically over the long summer break. But now a Harvard University study has come up with troubling indications that they also gain weight more quickly during those months when, traditionally, we hope they're outdoors much of the time, enjoying the summer sun.

In a statement that will make school administrators and lunch ladies across the land a little happier, Rebecca Franckle, who led the research, told me: "Despite the criticism schools face, something about that environment is actually promoting healthy growth opportunities."

Franckle's research, which compiled and analyzed the results of seven studies that have delved into this issue and was released Thursday in the Centers for Disease Control and Prevention journal Preventing Chronic Disease, has several important limitations (more about that later). But it does provide hints that kids in the 5-to-12 age range may be more sedentary, spending more time in front of television and computer screens and eating more fattening snacks when they leave the structured environment that school provides each day. Their sleep patterns are also probably less regular.

Especially vulnerable are kids who are already overweight or obese and poorer minority children. Low-income kids, the study speculates, have less access to summer camps and other places where they can get some exercise.

Many low-income children depend on school breakfasts and lunches for a significant portion of their calories during the nine months of the school year, and in recent years, federal and state mandates have forced improvements in the quality of some of those offerings. Franckle, a doctoral candidate in Harvard's School of Public Health, said something in the schools is promoting access to healthier foods and/or more exercise.

Wow. You wouldn't have seen that remark when I was in school eating microwaved pizza.

Franckle and her colleagues looked at seven studies of summer weight gain among children in the United States, Canada and Japan, and they found six that showed it accelerated for at least some of the kids. The researchers noted that while there has been extensive research on school-based interventions that aim to improve children's health, they actually spend 185 to 190 days each year outside of school.

Now about the limitations of the research: The small number of studies available for review makes the conclusions "tentative," the researchers wrote. Kids in this age range are growing, so it's more difficult to assess their weight gain than the weight increases of fully mature adults, though the researchers did note the use of a complicated formula to control for that in some cases. In Japan, where there was no weight gain seen, the summer break is only about 40 days long. And the research Franckle reviewed was conducted in different ways; some of it looked at anti-obesity programs that failed to provide a clean association between summer and weight gain.

Nevertheless, Franckle and her team suggested that poor kids be given even wider access to programs that will promote outdoor exercise, including opening up schools during the summer. Summer nutrition programs should also be expanded, she said.