There’s two huge problems with this.
One: Measures like this further ostracize the last group it’s okay to pick on – overweight people. There’s enough bullying going on in schools these days already (and really, if you need me to provide links you’re not paying attention). Visibly marking kids as different effectively makes these kids targets.
Two: The BMI is bullshit. This has nothing to do with me being bloody fat now. I’m well aware of that, thanks. No, let’s take a look at four pictures of me (these span over a decade and are arranged chronologically, FWIW):
Yeah, in that last picture I’m fat. No argument there. Guess which ones I’m NOT overweight in, according to the BMI?
That’s right. Not a single fracking one of them. According to the BMI I was overweight in EVERY SINGLE PICTURE ABOVE. I’ve been under the BMI’s “overweight” index once in my adult life, and it was rather scary what I had to do to get there. (It was unhealthy, let’s leave it at that.)
Promoting health? Absolutely. Working to get kids more active? Behind it 100%. Using a blunt, ineffective tool that will also make kids targets? Screw that.