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Editor's note: Ruben Navarrette is a CNN contributor and a nationally syndicated columnist with the Washington Post Writers Group. Follow him on Twitter @rubennavarrette.

(CNN) -- The parents of elementary school students in 19 states -- including Arkansas, Illinois, California and Massachusetts -- are receiving letters regarding something that really isn't a school's business: their children's weight.

School dieticians measure students' height and weight and then factor in age, and presto! They are able to compute students' Body Mass Index.

Schools can't afford foreign language courses, sports programs or music classes. But they found funds for dieticians?

Besides, the hocus-pocus they're practicing is not an exact science. There is a big argument going on among doctors and scientists as to what a BMI really means. For one thing, in measuring body mass, it doesn't distinguish fat from muscle.

Nevertheless, if a child is found to have an unhealthy BMI, his parents get a letter from the school informing them that their child could be obese.

And what do students call these notes? "Fat letters."

Oh, that's lovely. It makes you wonder what kind of people are teaching your kids. Many educators today might have a handle on math, science and reading. But they're flunking compassion, empathy, tact and sensitivity. Kids already have to put up with bullying from other kids at school. Now they also have to ward off insults from the adults who work in those schools?

And this isn't just happening in elementary schools. That's bad enough. These letters recently showed up in Southern California at a preschool. That means the students being weighed and measured were between 2 and 5 years old.

Imagine someone labeling a 2-year-old child "obese." These people are daffy. These "fat letters" belong in the trash can.

In Massachusetts, state lawmakers are considering a bill that bans schools from collecting students' BMI information.

The grade-school busybodies have the nerve to claim they're doing the labeling for the good of students and parents. The educators say they're bringing parents' attention to a potentially harmful situation.

That's spin. Why not just be honest and admit that this isn't about helping people; it's about what "nanny schooling" is always about: power and control.

The breach between teachers and parents is real, and it is as wide as ever. Whenever they're criticized for poor student performance, the first thing many teachers do is blame parents for not making sure that kids do their homework or not making education a priority at home. These public school weigh-ins, and the letters that get sent home, just give morally superior teachers more ammunition to fire at parents.

It used to be "you're a bad parent because you don't read to your child." Now it's "you're a bad parent because you let your kid get fat."

Don't they think that parents know whether their children are overweight and that the children know it, too? Do we really want to encourage a trend we already see: children going on diets? According to a study by Duke University, more than 40% of 9- and 10-year-old girls have gone on a diet.

To think, many of the public school educators -- and the dieticians in league with them -- actually consider themselves to be more enlightened than the rest of us. That's why, ironically, many of them have spent so much time over the years insisting that we must not label children over their academic performance.

They had a point. Schools have been slapping labels on students since before the invention of chalkboards.

In the 1960s, if you had looked through the school records of Mexican-American kids attending poor districts in Texas, Arizona or California, you would have probably found the letters "MR" next to many of their names -- for mentally retarded.

Later, as the self-esteem movement was catching on, students who might have once been labeled "lazy" simply became "unmotivated." Immigrant students who were once considered "limited English proficient" became "English learners."

My wife is a former teacher and a language therapist. She works with students who have dyslexia. The first thing she struggles with in evaluating a student, and preparing a course of study, is convincing parents not to be afraid of the "d-word."

The kinds of students she helps were once said to have a "learning disability." We don't say that anymore. Today, acknowledging that human beings process information in a variety of ways, we say that these kids have a "learning difference."

There you go. Academically, the enlightened view nowadays is that all students are different, that their brains are all wired in unique ways, and that's wrong to try to assess them with a one-size-fits-all yardstick and set rigid standards to determine who is intelligent and who isn't. The new consensus is that children's brains come in all shapes and sizes.

So why not be really enlightened and learn to think the same way about children's bodies?

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The opinions expressed in this commentary are solely those of Ruben Navarrette.