It might be time to reconsider the lunchbox.

A new study (pdf) carried out by researchers at Virginia Tech concluded that preschoolers and kindergartners tend to eat healthier lunches when the food is chosen by their school, not their parents. The study, which surveyed more than 1,300 lunches at three schools in Virginia, found that parents frequently pack things like chips, sweets, and sugary drinks—all of which are not allowed under the National School Lunch Program.

"I wasn't expecting there to be such a strong difference between school meals and lunches packed by parents," said Alisha Farris, one of the study's authors. "We thought that parents would send lunches that reinforced the sort of healthy habits we hope they are trying to establish at home."

Parents, it turns out, appear to do just the opposite. More than 60 percent of meals packed at home had one dessert (nearly 20 percent had two or more); just under 60 percent had savory snacks, like chips; and roughly 40 percent had a soda or sugar-added juice. School meals, meanwhile, were more likely to contain fruits, vegetables, naturally sweetened juices, and milk.

The study is careful to acknowledge that the sample observed isn't nationally representative, but there's reason to believe the problem is hardly limited to parents who send their children to public preschools and kindergartens in Virginia. A similar study carried out in Massachusetts this year found a similarly troubling pattern for elementary school students. "Lunches were comprised more of packaged foods than anything else," senior author Jeanne Goldberg said in a statement.

Farris suspects the same. "The packed lunches that children all over America are eating might very well look like this," she said.

A great deal of effort and attention has been directed towards improving the food served at public schools around the country, which might help explain why packed meals perform so poorly by comparison from a nutritional standpoint. The most recent overhaul of the National School Lunch Program, which took effect this year, set strict guidelines on servings of fruits, vegetables, and other healthy foods, while discouraging the inclusion of unhealthy snacks and beverages, like sugar-sweetened juices, sodas, and chips (well, for the most part).

What children eat for lunch, and at school in general, is important because it tends to comprise a substantial portion of the calories they consume throughout the day—between a third and one half of daily calories, on average, to be more precise. For roughly 40 percent of the children, those lunches are packed by their parents, and, often it seems, rather poorly. For the remaining 60 percent who eat what food their schools provide, they appear to be getting more nutritional meals.