My son just brought home a sheet from Cub Scouts asking him to track everything he eats and each item's calorie count, something we consider a disordered eating behavior around here. (We won't be doing it. Calls will be made.)
I do not hold to the idea that these influences cause eating disorders - I think the vulnerability is pre-existing and set in motion or triggered by dieting, overexercise, or illness. But these wrong-headed lessons can trigger those triggers, and are particularly counterproductive for children in recovery, and create a hostile environment for them when other kids are taught to parrot this stuff.
My son says "all my teachers talk about calories all the time and getting fat."
Parents of kids with eating disorders often have their children pulled out of health classes, body fat testing, BMI checks, and other "triggering" experiences. I think this isn't enough. We ALL need to pull our kids from these anti-scientific lessons for the sake of all children.
There is no evidence that the kids who take these messages to heart are in need of them in the first place. There is no evidence that these "classes" change weights or behaviors in the long run - except in precipitating unhealthy dieting behaviors. "Do no harm" should apply to education, too.
(postscript: you may want to check out blogger Sandy Szwarc's post on this topic:HERE.)