Weight per se is a very poor indicator.
You only need witness that strong man's links.
If you wanted to introduce a system that meant you were referred to a dietitian and a cardiologist and a life-style coach (etc etc add as you feel necessary) you'd be in with more of a chance if it was worked out on % body fat and in particular, visceral fat levels.
Look at the previous link. In the survey, 4 out of 5 parents with overweight kids did not know their kids were fat / obese.
Therein lies the crux of the problem, in a nut shell.
Blame? Parents
There was a R4 interview on / about 30 Dec highlighting just this. I've been searching for the link without success.
There's a long running study being carried out in the S'hampton region, and it's throwing up some fascinating, and as yet, not full understood results, pointing the finger at parents being the single biggest contributor to this problem.
It seem if you were over-fed between 1-5yrs old, that's your likely body shape for good.
Like I say, it's on-going and made fascinating listening.