A growing initiative by some schools across the country has students and parents up in arms: the school are measuring students at an annual weigh-in, and sending reports home telling parents whether their child's body mass index is healthy or dangerous.

Hope Green, who has two school-aged children in upstate New York, said children are placed under too much stress at school.

"The last thing they need is the school to now step in … 'You're too skinny,' 'You're too fat,'" she said.

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Schools in 19 states, from Arkansas to Illinois, participate in the annual student weigh-ins. Some pediatricians say body mass index (BMI) readings are helpful in combating childhood obesity, which is a growing problem.

Right now, BMI readings are "the best means we have to determine whether a child's weight is healthy or unhealthy," said Dr. Lanre Omojokun Falusi, a Washington, D.C.-based pediatrician and a spokesperson for the American Academy of Pediatrics.

But some eating disorder experts worry that taking the readings may do more harm than good.

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"I would like to see BMI testing in schools banned," said Claire Mysko of the National Eating Disorders Association. "For those who are already insecure about their weight, these tests can … potentially trigger an eating disorder."

Experts are concerned about the potential for eating disorders in girls and boys, but are especially concerned about girls given that girls are more likely than boys to experience such disorders.

More than 40 percent of 9- and 10-year-old girls have already been on a diet. As many as 60 percent of all children between the ages of 6 and 12 years old are worried about their weight, according to Duke University.

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Some children who get the "fat letters" - as students themselves call them - are as young as 6 or 7 years old.

Lucy Williams attends a public middle school in New York City. She says she's "insecure" because she's taller than a lot of her fellow students.

"And I'm also bigger than a lot of them," the 13-year-old said. "I'm not incredibly skinny."

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"Good Morning America" talked to other students who share Lucy's concern.

Of the BMI reports, Zuzu Park-Stettner, 13, who also attends public school in Manhattan, said: "I hate them."

Added her sister, Jane Park-Stettner, 9: "If they knew how much you weighed and if it was a really high number, like 100 … it would cause bullying."

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Jane and Zuzu's mother, Shannon Park, is also concerned about the effects of measuring students' BMIs, especially for students who are entering adolescence.

"Their bodies are changing … And then they get this number that says, 'Oh, you know, you're not the right number.' It's just a horrible way to start womanhood," she said.