The findings take on extra importance when one considers that more than 40 percent of school kids bring lunch.

When researchers asked more than 600 third- and fourth-graders at 12 undisclosed public schools in eastern Massachusetts to empty their lunch boxes, packaged foods and sugary drinks dominated — potato chips, fruit drinks, cookies.

"Gummy fruit [snacks] were very common," Hubbard said.

Nearly one in four lunches lacked an entree, such as a sandwich or leftovers, and instead were made up of packaged snacks and desserts, according to the study, which was published in the Journal of the American Academy of Nutrition and Dietetics.

The few studies that do exist on packed lunches, the Tufts researchers noted, found that children who bring lunch generally eat fewer fruits and vegetables — and more calories — than those who participate in the National School Lunch Program.

With the first day of school arriving all too soon, many parents are not looking forward to the challenge of packing a lunch that is healthy, enticing, and reasonably priced — day after day after day.

Fiona Healy, a math coach in Cambridge, says she can make a respectable lunch at the beginning of the week, “but come Wednesday, things start to fall apart.”

Her 8-year-old daughter, Brenna Walsh, will eat fresh deli turkey, most of the time, but that requires a frequency of grocery shopping that the working mother cannot maintain, and her daughter does not like much else that’s healthy. Many days, Brenna eats the pretzels and cookies her mom packs as a treat and ignores the meal.

“The strawberries come back in their neat little container,” Healy said. When she asks what happened, their conversation will be familiar to many parents.

Brenna: “I didn’t have time.”

Mom: “But you had time to eat that bag of pretzels and cookies.”

It is the rare parent who does not care about nutrition, but vitamins and nutrients are often only one of a parent’s many goals, said sociologist Dina Rose, the author of “It’s Not About the Broccoli: Three Habits to Teach Your Kids for a Lifetime of Healthy Eating.”

“They don’t want their kids to be hungry,” she said. “Or they don’t want to have conflict, or they want them to be happy, or they’ve got 12 other kids, and other things going on in the morning.”

There are many ways to go wrong with lunch, Rose says, but one of the insidious is what she calls the “at least” strategy.

“Parents make the ‘at least’ compromise,” she said. “ ‘At least’ chocolate milk has calcium. ‘At least’ chicken nuggets have protein. If you think of the cumulative effect of the ‘at least’ mindset, we’re teaching our kids the exact opposite habits we want them to have. We’re dumbing down their diets, and more importantly, we’re pushing their taste buds towards junk and away from healthy foods.”

The Tufts study showing the shortcomings of home-packed lunches comes in the wake of controversial mandated changes to food served in school cafeterias. Starting in 2012, public schools were required to serve more fruits and vegetables, and less salt and sugar, in compliance with the United States Department of Agriculture’s new standards.

But the new requirements — passed after a compromise on potatoes that didn’t restrict how often they could be served — remain a matter of contention. In January, the General Accountabilty Office reported that kids were so unhappy with all that nutrition that they were buying fewer meals at school.

“Nationwide, student participation in the National School Lunch Program declined by 1.2 million students [or 3.7 percent] from school year 2010-2011 through school year 2012-2013,” the GAO report noted. “State and local officials reported that the changes to lunch content and nutrition requirements, as well as other factors, influenced student participation.

But the GAO study was hardly the last word. In May, Michelle Obama went after members of the House of Representatives whom, she says, are trying to undo some of the healthier changes. “They want to make it optional, not mandatory, for schools to serve fruits and vegetables to our kids,” she wrote a New York Times op-ed.

In July, the journal “Childhood Obesity” reported that despite initial complaints, public school kids seem to be accepting healthier public school meals.

As the public debate continues, so do the private ones.

A recent Sunday afternoon found two friendly combatants, Erin Martinez of Allston, and her 7-year-old daughter, cruising the back-to-school aisles at Target.

“She’s a vegetarian,” Martinez said, gesturing to Devi, who was sitting in the cart amid notebooks and other supplies. “So I’ll pack her rice and beans.”

But often Devi ignores her mother’s complete protein in favor of a hamburger bun her school is serving (along with a burger, which she skips).

“It’s a waste of food,” Martinez said, projecting herself unhappily ahead to this year’s lunch issues.

Devi felt no such stress. “I like bread,” she said, smiling sweetly.