Tony Cenicola/The New York Times

Is chocolate milk a healthful choice for schoolchildren?

Some nutritionists say chocolate milk is a perfectly fine snack for students, one that provides much-needed calcium and vitamins, and is a healthy alternative to sugary juices and sodas. But others say flavored milks, with their added sugars, contribute to the childhood obesity epidemic. Some school districts have tried removing flavored milk from their cafeterias entirely, but studies show that many students simply skip milk altogether when they do not have flavored milk as an option.

Now parents who are concerned about the amount of sugar their children are chugging in school cafeterias may be encouraged by an announcement from the milk industry. Starting in September, chocolate milk will have fewer calories and less sugar.

The eight-ounce cartons of fat-free and low-fat chocolate milk served in schools will have 38 percent less added sugar and just 31 more calories than regular white milk, said the Milk Processor Education Program, or MilkPEP, the industry group that runs the national “Got Milk?” campaign. On average, cartons of flavored milk will contain less than 150 calories and 22 grams of total sugar this year, the group said.

The changes will affect a vast majority of the nation’s school districts. A report by the School Nutrition Association last week found that almost 96 percent of school districts offer students flavored milk, and all but 2 percent offer fat-free milk.

The issue of flavored milk has been highlighted by the chef Jamie Oliver, who railed against chocolate milk and processed foods in school cafeterias in his ABC television series, “Jamie Oliver’s Food Revolution.” On his Web site he notes that one serving of chocolate milk has four teaspoons of added sugar.

“When kids drink chocolate and strawberry milk every day at school,” he writes on the site, “they’re getting nearly two gallons of extra sugar each year. Too much sugar is threatening the health of our kids and we’ve got to do something about it.”

This year, in the face of mounting pressure, the Los Angeles Unified School District voted to ban chocolate and strawberry milk entirely from Los Angeles public schools. The district’s board of education voted 5 to 2 to remove flavored milk after intense pressure from Mr. Oliver and parents of children in the district, some of whom held protests outside the district’s headquarters organized by the activist group FoodForLunch.

Whether the taste of the new, leaner varieties of milk will have any effect on how much milk students drink remains to be seen. One study by MilkPEP in 2009 looked at what happened when 58 elementary and secondary schools in seven districts around the country removed flavored milk from their cafeterias, either entirely or only on select days of the week. The study found as a result that milk consumption among elementary school students fell by 35 percent. The average daily consumption of milk per student, meanwhile, fell to four ounces at schools where only white milk was offered. At schools where all flavors were offered, it stayed at six ounces per student.

In a statement, MilkPEP said that taking away low-fat chocolate milk — the most popular milk choice in schools — would mean students would get “fewer essential nutrients.”

“Whether plain or flavored, milk contributes so many vital nutrients to a child’s diet,” said Vivian Godfrey, the group’s chief executive, “and we want to do our part to be sure the milk on the tray is enjoyed and actually consumed with the meal.”