Once a year many kids come home from school gripping a different kind of report card. The missives do not list “A’s,” “B’s” or something less. Instead, the reports, informally dubbed “fat letters,” rate how children’s body mass indexes (BMIs) compare with those of other kids their age. 

Many children are receiving poor marks. That’s not too surprising when you consider that more than one third of children and adolescents are overweight or obese. The fat letters are designed to help nudge parents of these children to make some healthy changes. There is some evidence that the letters may increase parents’ awareness of the importance of health and weight issues. Yet solid proof is lacking that the reports help obese children lose pounds.

That absence of good data continues to irk critics who say collecting such health info should be left to kids’ doctors and parents. Some also complain about educators spending even a nominal amount—perhaps $60 to $500 a year for each school—when programs from music and art are under cost pressure and there is scant evidence the expenditure is making kids healthier. The letter dust-up has also sparked the first-ever randomized control trial to test the effectiveness of a practice that is now in place in nine states. But even if definitive answers are lacking, it is clear the letters have drawn the attention of their recipients.

They do seem to influence parental perceptions of their child’s weight and health. A year after parents in Arkansas read the letters, a survey found that parents were more likely to accurately describe their child’s weight status (that is, overweight or healthy weight). Another study in Massachusetts looked at the health report cards and found that parents receiving the letters were significantly more likely to know their child’s weight and take steps to address it.

Without interventions like the letters parental misconceptions about childhood weight are common. Multiple studies have concluded that most parents generally believe their children’s weight is normal when it is not. In one survey about three quarters of parents of obese preschool-age kids said their children’s weight was “just right”—part of a larger trend in which being overweight is viewed as the new normal. “It makes it harder to point out there’s a problem if society alters how we characterize what’s big and normalizes a larger size,” says Jeffrey Koplan, a professor of public health and medicine at Emory University.

In 2005 an Institute of Medicine (IOM) panel chaired by Koplan first recommended that schools should notify parents about their kids’ body mass index, a calculation of height-to-weight ratios.  The panel was tasked with thinking about how to best combat childhood obesity and they started to think about how schools could help. Other school-based testing, they knew, was used to assess vision or hearing. Maybe BMI could be the next frontier.

The response to the letters, however, has been mixed at best. They do not always make it into parents’ hands. And when they do, parents may not read them or understand their implications. Other times, they spark outrage: parents have reported the letter contents were not kept confidential, their kids were bullied due to the ratings or that they prompted body issues among their children. Massachusetts dropped its statewide program after three years, citing concerns about confidentiality and its inability to monitor how schools communicated this information to parents.

Some parents, however, have reported in follow-up surveys that they have changed their child’s unhealthy snacks or exercise levels after reading the letters, which is a step in the right direction. Still other research suggests most parents do want the letters.

Beyond research on problems with how the letters were written or delivered, however, answers on whether they actually help kids lose weight continues to remain unsettled. Arkansas was one of the earliest states to adopt such notifications. In 2003 (even before the IOM recommendation) it rolled out a requirement not just to test for BMI but to then send letters to parents describing the findings. Since the statewide notification program was put in place BMIs have stopped increasing—remaining at their plateau.

Is that change due to the letters? It is hard to pin down. One reason: the letters were not the only action the state took to combat childhood obesity. The state also launched a variety of programs designed to help kids eat healthier and exercise more at school. Further complicating matters: Arkansas’s BMI trend largely mirrors a nationwide freeze in childhood BMIs, too. That may reflect greater national consciousness about childhood obesity and changes in behavior. But, again, it’s hard to say.

Zeroing in on BMI scores as the lone marker of success may be misguided, asserts Dominique G. Ruggieri, a University of Pennsylvania researcher who has studied the letters. “There are other measures of success,” she says, pointing to drops in vending machine sales in schools following the intervention in Arkansas and to reports of more physical exercise among kids there.

Looking for harder evidence, researchers have launched the first randomized control trial to consider whether “fat letters” can make a difference. Kristine Madsen, an expert on childhood health and disparities at the University of California, Berkeley, heads the study, which includes 75 schools across California that have been divided into three groups. The first group will not be conducting any annual fitness exams that include height and weight measurements. The second group will have such fitness tests but the data will not be sent home to the students or their parents. The third group will carry out the tests and subsequently parents will receive one-page letters to describe what the tests found. The letters will detail if the BMI measurements suggest a child is underweight, an appropriate weight, “at risk of being overweight” or already “overweight.”

The three-year study, which began last year and is funded by the National Institutes of Health, includes third through eighth graders. “I think this randomized study being carried out is an important step forward, but how do California results generalize to other states?” asks Kevin Gee, a professor of education policy at the University of California, Davis, who recently studied whether the Arkansas BMI letters show any benefit among high-school-age kids whose parents had previously received letters when the students were younger—they don’t. Right now, he says, different states screen for BMI at different grades and there is no consistency in processes or even what the letters say.

But new data suggests that in some cases, telling people they are overweight can backfire—fueling further unhealthy behaviors. A study published in the International Journal of Obesity that included U.S. and British adults found that when individuals believed they were overweight, it led them to eat more. In addition, the finding was true regardless of whether the person was actually overweight or not. The study authors concluded that perceiving oneself as being overweight was linked with overeating in response to stress, which fueled future weight gain. Madsen, who was not involved with the research, says that overeating may belie a “sense of hopelessness.” The new finding, she says, could also be applicable to kids because “there is stress in knowing or feeling you are overweight and body dissatisfaction.”

For his part, Koplan, whose panel recommendations originally fueled many of the letters, is skeptical that the letters can trigger much change on their own. “The things that tend to work, whether it be tobacco control or dietary change issues, are interventions with multiple components that occur at multiple times of the day in a multiplicity of settings,” he says. Just taking one component like a letter “is, to my mind, a highly weak, deluded approach to changing attitudes and behaviors. You need a much stronger package of interventions.”