Child obesity rates drop in Mass.

Declines — reported by roughly three-quarters of school districts — were greatest among elementary school students.

“This is now a trend, and we are working hard to see that it continue,” said Carlene Pavlos, director of the health department bureau that runs the school screening program. “This is not the time to let up on our strategies and interventions.”

Researchers are still analyzing the data — based on annual weight and height screenings — to determine which of many school- and community-based nutrition and physical activity programs may have had the greatest impact, she said.

The findings come as state regulators agreed to scrap controversial letters schools send parents about their children’s weight, after years of complaints that they lead to bullying and excess costs for schools.

Massachusetts began requiring schools to measure students’ height and weight in 2009, and to notify parents of the results, as part of a larger campaign aimed at reversing the obesity epidemic. Nearly a third of all US children are overweight or obese.

Researchers at the state health department, along with scientists from the University of Massachusetts Medical School, analyzed nearly 1 million student weight and height records from 290 districts. They found wide variations across the state, with 9.7 percent of students obese or overweight in one district at the low end, and 69 percent of students at the high end.

The data show that obesity levels over the five-year period were highest in poorer households. But a federal report in August suggested that even in this population the trend was promising: obesity rates declined among preschoolers from lower-income families in Massachusetts and 17 other states from 2008 to 2011.

The state data also show that boys were more likely to be heavy, with 33.9 percent overweight or obese compared with 30.8 percent of girls.

Independent nutrition researchers said the early results are encouraging.

“These data show that obesity doesn’t defy the laws of common sense,” said Dr. David Ludwig, director of the New Balance Foundation Obesity Prevention Center at Boston Children’s Hospital. “You get rid of sugary drinks from schools, improve the quality of school lunch, promote regular physical activity, and children’s body weight responds.”

But Ludwig said kids are still exposed to a “toxic” social environment, laden with advertising for everything from “sugary beverages to Lucky Charms.”

He said the Massachusetts data suggest that the state has reached a new stage in the childhood obesity epidemic in which the rapid year after year increases have plateaued. “But we will need much more substantial declines before we can put the champagne on ice, let alone pop the cork,” he said.

Dr. Caroline Apovian, a Boston University School of Medicine professor, said she treats many families who can’t afford healthy foods, and often resort to pizza and other fat-laden choices because they are cheaper. Her clinic writes “prescriptions” that allow low-income families to receive free vegetables, fruit, and other healthy foods at Boston Medical Center’s food pantry.

“We need to continue all of these efforts,” said Apovian, who was traveling in Armenia, where childhood obesity levels are rising rapidly.

“They are where we were 20 years ago or more,” she said. “People around the world can now see that these [anti-obesity] efforts are finally seeing fruition in the United States.”

The decision to eliminate school letters to parents was made by the Public Health Council, an appointed body of academics and health advocates that sets regulations. Schools will still have to conduct student weight and height screenings in grades 1, 4, 7, and 10, to help officials gather data about obesity trends and identify possible solutions.

Schools complained that it was too expensive to mail the letters as required, so they often sent them home in students’ backpacks. That sometimes led to inadvertent disclosure of the information to other students and teasing, officials have said.

In addition, such letters, intended to foster conversations between parents and their child’s physician, appear not to help stem childhood obesity rates, according to a 2011 study of a similar program in the California public schools.

The new rules eliminate the required parental notification and instead allow school districts to make the information available to parents or guardians upon written request.

To address parents’ concerns, regulators added a provision that will allow local school committees or boards of health to adopt extra requirements to “ensure confidentiality.”

Massachusetts is one of 21 states that routinely measure school-aged children’s weight and height, according to the health department, but only nine , including Massachusetts until now, sent letters home.

Kay Lazar can be reached at klazar@globe.com.