School programs to monitor students' weight and send updates home have almost no effect, a new study finds.

Schools in 10 states are required to send these notifications -- so-called "fat letters" -- home to parents. In 2003, Arkansas became the first state to implement this type of program, The New York Times reported.

This study of high school juniors and seniors in Arkansas found that students whose families received the updates showed no notable improvement in body mass index (BMI - an estimate of body fat based on height and weight) scores after two years, compared to those whose families did not receive the updates.

The study in The Journal of Adolescent Health raises questions about the use of the letters.

"The typical 16-year-old's reaction to getting a letter at home and having your parents tell you to eat right and exercise, would be, 'Don't nag me,' " study author Kevin Gee, assistant professor of education policy, University of California, Davis, told The Times.

A 2011 study of younger students in California yielded similar findings about the use of such letters, and many health, parent and educator groups oppose such programs.

"There is so much stigma with being overweight, and children in adolescence are particularly sensitive to that," Mary Story, an expert on teen obesity at Duke University, told The Times. "In some schools, there is no privacy screen when they're being weighed, and the process is embarrassing for them."