And one mother fighting back, after her daughter came home from school with a body mass index letter labeling her as overweight. Abc's bianna golodryga has that story for us. Reporter:11-year-old lily... See More
And one mother fighting back, after her daughter came home from school with a body mass index letter labeling her as overweight. Abc's bianna golodryga has that story for us. Reporter:11-year-old lily is on the school volleyball team and eats healthy foods. You want to get them out of the refrigerator? Sure. Reporter: She was stunned when florida health officials sent a letter suggesting she's fat. This whole thing is stupid. It can hurt people. It can break their courage. Report First, I was hurt. Then, I was angry. Then, I just was concerned. Reporter: The so-called fat letter, is the result of a body mass index screening, given to lily by officials at school. To give a kid a letter that the rest of their life they may be overweight or obese the rest of their life because of a measurement you took one day, it's not fair. Reporter: Similar screening programs have been embraced by schools. They're a great idea. I hope that all parents can become aware. Reporter: But eating does order experts worry the screenings do more harm than good. I would like to see bmi testing in schools banned. These tests can trigger an eating disorder. Reporter: A panel of girls i spoke with, told me they dread the screening. I know all of your schools have a bmi reading now. How do you feel about them? I hate them. It doesn't do much for people, except for make them more insecure about themselves. Reporter: Florida officials refused to speak on camera about lily's report. In a statement, they said the screenings, quote, provide valuable information to parents and help ensure that students are healthy and ready to learn. As for lily, she says she hasn't let the letter affect her and has learned an important lesson. I'm confident in everything that I do. And never give up. Reporter: For "good morning america," bianna golodryga, abc news, new york. And for more, joining us, abc news chief and health editor, and practicing pediatrician, rich besser. We see lily in this piece. Active. Doesn't appear to be overweight at all. How accurate are the tests? The bmi, is the best measure we have for being overweight or obese. But it's a screening test. There's certain people, when you're going to run a little high. If you're muscling -- professional athletes on every scale will show up as obese. You look at them in the mirror and say, you're fit. Here, if they talk to the doctor, the doctor would have said, your child is in great shape. It's going to come up heavier than that. But there was something in the letter, that she was trending overweight. That's the whole point here. You want to pick up kids before they become obese. And the letters go to every child in the school, to say their height, their weight, their bmi. Is their weight trending heavy or are they overweight? Once a child is obese, it's so hard to undo that. Every time I see a child, i measure this. If they're starting to cross percentages, they're in the 50th Percent, now 70 and then 80, you want to talk about exercise because you can make a difference. Emotionally, physically, these kind of screenings -- I think it's good. It has to go to every parent. We screen hearing, vision, teeth, immunization. This is more important than any of those. And many children after they start school, they don't come back to their doctor. Everyone gets this. Everyone gets it. Everyone needs to get it. Not just children who are overweight. And it's a screening. It's a screening. The letter says go back to your doctor and talk about this. As they do with a hearing test or an eye test. You don't say go get glasses. You say go to your doctor. Eyes and the ears. Those are things you need to learn. There is -- even if everybody gets its, there's a degree of shame attached to these. And it's hard enough to being a schoolkid. Well-intended. But I'm not sure that a school system had ever changed a social trend. The first state to implement this, arkansas, they saw a rise in activity programs. You have to see over time. If it's doing that, ooh it's a good thing. And arkansas is the first one. They know about childhood obesity, in the southern states. They wanted to do something about it. 19, 21 states now doing it. It's great that it causes this kind of discussion. Yeah. Thanks, rich. Next up, the "gma heat
This transcript has been automatically generated and may not be 100% accurate.