My son is 5'6" and weighs 152-153 pounds. I think he could lose 3-5 pounds easily, but he is not much over-weight. I have a tough time convincing some people that he is only 10. At football state last year his age was challenged. I am not saying he is all muscle, he does have some table muscle too!!
You do make a good point that just changing some of the kids' eating habits can drop 5 pounds or so. Actually at this age I think some kids' weight can change by 3-5 pounds over a week depending on how much Kool-aid and after school "snacks" at consumed.
But I do not feel like my son is enough over-weight to put him on a diet, he is just a big kid over all.
Hopefully someone who has seen him can back me up that he is not too overweight??!!??