I think type 2 diabetes is relatively uncommon amongst children. Obviously, with increasing body weight, the risk goes up, but most of the children would not acquire it until their late 20s or 30s.
I do think monitoring weight, particularly waist circumference, is important, but I think it needs to be anonymized. You don't want a child going home with a relative body mass index on their report, as is being proposed. You need to be thinking in the longer term, two or three years down the line, and not expect to see results in six months or one year, but at least be able to stem the proportion of children who are above one of the cut-off points. Relative body mass index is quite good for groups of children, but it's not very good for defining whether individuals are specifically overweight. Some children are more muscle-bound; others have relatively more fat, and fat is lighter than muscle.