A Florida mom is outraged today over an unpleasant letter she received in the mail from her daughter's school.

The letter told Kristen Grasso that her 11-year-old daughter, Lily, was overweight.

"Lily is tall, she's athletic, she's solid muscle," Grasso said to Fox 4 News. "By no means is she overweight."

Her daughter's middle school came to the determination about her weight through a BMI health screening, which is mandated by Florida law, but does allow parents to opt out. Grasso believed the screening would be for vision and hearing tests, and not weight.

Approximately 20 states have adopted new mandatory health screenings, which include weigh-ins to calculate a child's BMI, as part of a nationwide effort to combat childhood obesity, according to Yahoo! Shine. Over the last 30 years, the rate of obese children in the U.S. has more than doubled, while the rate of obese tens has more than tripled.

BMI is calculated by dividing a person's weight in kilograms by height in meters squared, and has long been widely used by doctors to determine weight problems. The Centers for Disease Control says that children whose BMIs are in the 85th to 95th percentile are considered overweight, while those over the 95th percentile are deemed obese.

However, these tests then result in the children who screen as overweight being sent home with these "fat letters." Parents, including Grasso, are concerned that these will lead to self-esteem issues and possible bullying.

Lynn Grefe, the president of the National Eating Disorders Association, spoke out against the issue, saying that these BMI report cards can lead to bullying and could encourage the unhealthy behaviors that later lead to eating disorders.