Amy Oztan is one of thousands of parents who got a letter from school bluntly pointing out that her son is fat. She promptly threw the letter away.

“My son, who is very tall for his age and is a little husky, but fit, brought home a piece of paper from his school listing his BMI and stating that he was obese,” said Oztan, a New York City mother of two.

“I ignored it, because anyone looking at him would laugh at that assessment,” said the 37-year-old who writes for NYC Mom Blog. “But when my husband saw it he freaked out a little bit.”

Soon, many more children might be routinely subjected to the fat police and a one-size-fits-all measurement of health - the body mass index or BMI - as health experts and politicians attempt to deal with the childhood obesity crisis.

BMI, a simple formula that compares a person’s weight and height, is the most widely used tool to screen for weight-related health problems and is recommended by the American Academy of Pediatrics for all children and adolescents.

Though some individuals are exceptions, the BMI can prompt doctors for further test for an absolute diagnosis of obesity.

Just this week, researchers from the nonprofit Altarum Institute published an analysis in Health Affairs magazine, calling on states to implement an electronic BMI surveillance system.

The report is part of the Altarum Institute Obesity Prevention Mission Project, which has responded to first lady Michelle Obama’s “Let’s Move” campaign to promote regular screening of all children’s BMI.

Researchers say public health surveillance through immunization registries - a model being implemented in Michigan and in San Diego County, Calif. - could be a cost-effective way to provide needed data and help determine how resources are allocated.

Doctors would measure children’s BMI and enter data in established immunization registries that often include additional data like newborn hearing tests and lead exposure.

Oztan insists the BMI is a “minefield” when it comes to evaluating health and state surveillance would be a “dumb idea.”

“I see thin kids walking to my kids’ school eating Cheetos for breakfast, and those kids wouldn’t get targeted by this program,” she said. “My son takes tae kwon do four days a week and can run faster than any kid in his class, but he would be targeted.”

And doctors, who are on the front lines, say that the BMI battle alone may not be enough.

“My admonition is not to lull ourselves selves into thinking just BMI gives us a solution,” said Dr. George Flores, senior program officers of The California Endowment, a community-based health foundation.

“Environment and behavior are the things we need to pay most attention to,” he said. “If you just look at weight, you miss the more important issues of what need to be measured tracked and corrected - the things that lead to being overweight.”

Doctors say the problem is that children watch too much TV and play video games instead of going outside. Parents don’t model good eating habits and schools are cutting back on physical education programs and recess.

Childhood obesity has more than tripled in the past 30 years, according to the Centers for Disease Control and Prevention. The prevalence among children aged 6 to 11 years increased from 6.5 percent in 1980 to 19.6 percent in 2008. Among teens it jumped from 5 percent to 18 percent.

But Altarum researchers say data on children ages 5-14 are scarce and among children under 5, only those enrolled in public assistance programs are counted.

“The advantage of the registry-based clinical model is that it focuses on the youngest children - where we have the best chance of preventing obesity from developing in the first place,” said co-author and Altarum fellow Matt Longjohn.

“The clinical model also reminds providers to screen children and how to counsel them and their families according to established standards.”