What not to do...

...if you're trying to combat obesity, or "Lesson # 2536 about why units matter." Here's the scoop; public health people have been arguing that the best thing they can do to combat childhood obesity is to calculate "body mass index" (BMI, ratio of weight to the square of height, in kg/m^2) and warn parents if their child is over a certain ratio.

The problem is twofold; first of all, as the article indicates, children are susceptible to eating disorders when told they are fat. So the advice may be causing more problems than it solves to begin with.

Second, the correlation between BMI and health problems is tangential at best. Most of the NBA and NHL--no couch potatoes there--fail the BMI test, but are in excellent health. The real problem as far as health is concerned is primarily excess fat, and teachers are generally ill-prepared to diagnose this.

Of course, the one saving grace here is that, thanks to government education, 20% of adults are functionally illiterate, and their children will never know that they're considered fat.