CHULA VISTA, calif. — The Chula Vista school district not only measures the academic progress of Marina Beltran's second-grader, it also measures her son's body fat.

Every two years, Antonio Beltran, like his classmates, steps on a scale. Trained district personnel also measure his height and then use the two figures to calculate his body mass index, an indicator of body fat.

The calculation isn't reported to Beltran or her son, who cannot see the readout on the scale that has a remote display. Instead, it's used by the district to collect local data on children's weight.

Beltran supports her son's school in measuring students because the data have brought in help to address obesity, which can lead to diabetes and other illnesses tied to a lifetime of poor habits. But the practice hasn't been embraced everywhere.

Other school districts have angered parents and eating-disorder groups by conducting screenings to identify overweight children and send home what critics call obesity report cards or "fat letters."

Amid the nation's childhood obesity epidemic, schools in nearly a quarter of all states record body mass index scores, measuring hundreds of thousands of students.

Some, like the Chula Vista Elementary School District, do what is known as surveillance, in which students are measured to identify how many are at risk for weight-related health problems but they remain anonymous. Other districts track the weight of individual students and notify parents whose children are classified at an unhealthy weight.

Chula Vista is being touted for its methods that have resulted in motivating the community to take action. When nearly 25,000 students were measured in 2010, it discovered about 40 percent of its children were obese or overweight.

Officials used the data to make a color-coded obesity map of the district and showed the community. Instead of creating a stir, the information acted as a distress call, bringing in help.

Schools boosted partnerships with doctors. They planted gardens, banned cupcakes at school birthdays, and tracked kids' activity levels.

"I've seen a dramatic change," Beltran said.

Vicki Greenleaf said she received what she called a "fat letter" in the mail last summer from the Los Angeles Unified School District. Her daughter does Brazilian martial arts four times a week and is built like Olympic gold medalist Mary Lou Retton, but was classified as overweight by the state-mandated body mass index screening program, she said.

"I think those letters make kids feel bad about themselves," she said. "For a kid that is predisposed to an eating disorder, those are the kind of triggers that can set it off."

18%

Children in the U.S. who were obese in 2012

21%

Adolescents ages 12 to 17 who were obese in 2012

70%

Number of obese youths who have at least one risk factor for cardiovascular disease Source: Centers for Disease Control and Prevention