The state issued a new mandate for schools this year. Each school district has to calculate the body mass index - BMI - of students in the first, fourth, seventh and 10th grades. The kids will be called into the nurse's office, told to take off their shoes, and have their height measured. Then they'll be weighed. Using those numbers, the nurse will determine the BMI of the child or teenager and send the result home, along with advice on how parents can help overweight children slim down.

There is so much wrong with this plan I hardly know where to begin.

Understandably, some parents find the very idea presumptuous and offensive. Is there a parent who doesn't know if their child is overweight? Parents don't need the schools to tell them this. Yet the state seems to think parents are neglecting their children's well-being, and the parents are going to hear about it.

As for advice on losing weight, that information is all around us. A report from the school department will just rehash the common wisdom. Besides, if losing weight were as simple as reading a booklet, everybody would be slim.

The schools, meanwhile, are getting yet another mandate at a time when they're supposed to be focusing on English and math competency, which would seem to be a higher priority. The order to measure students' BMI comes with the threat of withholding funds, just what the schools need. As for the measurement process, how do you think the students will take this? Oh sure, the tests will be in private, but the kids know what's going on and will no doubt be making comparisons, along with jibes and jokes. By all means, let's make children and adolescents more self-conscious.

Now let's consider exactly what the state has told the schools to do. Each student will be pulled out of class, put through the measurement process, and then the nurse will determine the BMI. This requires a bit of arithmetic; or you could consult a height-and-weight table, or you could just plug the numbers into a calculator on the computer.

If you want to try it out, Google "calculate BMI." The top link is an automatic calculator from the National Institutes of Health. Enter height and weight and the BMI number pops up. Then you're given the scale that purports to tell you whether you're too thin or too fat. There are separate calculators or scales for children and teenagers. In other words, this is not something that only an expert can do.

But even if it were, the BMI is a lousy tool. It's a gimmick, really, putting the gloss of a supposedly precise number, decimal point and all, on a complicated health and behavior matter.

The BMI formula doesn't account for different body types, sometimes referred to as ecto-, meso- and endomorph, or the apple- vs. pear-shaped body. Thus the BMI number can be misleading. A male student athlete, for example, may have the BMI of a fat person when he is actually muscular with no excess body fat. Or a female student may be taller and heavier than average but carry the weight well.

There are better ways to determine whether a young person's weight should be of concern, because it is true that being overweight early puts one at risk of being obese later. There's the waist-to-hip ratio and the skin-fold test. (There are calculators on the Internet for these, too.) Then there's bio-electrical impedance analysis which involves sending a weak electric current through the body to determine lean muscle mass and body fat. Some home scales have this feature.

In sum, the state's plan is a complete boondoggle. Educationally it's out of the Dark Ages. It's an insult to parents and school boards. Scientifically it's lacking. It's a waste of time and money, an abuse of bureaucratic power and an affront to taxpayers.

Now that Massachusetts has universal health insurance, the schools should stick to teaching about health and leave doctors to advise parents if their children have a weight problem.

NED BRISTOL is a member of The Sun Chronicle Editorial Board and a former editor of the newspaper.