...some sort of manageable grouping is needed to make the point since this is a conversation and not an academic journal... True, you don't need to be quite so

...some sort of manageable grouping is needed to make the point since this is a conversation and not an academic journal... True, you don't need to be quite so formal here, but can you really say that you've "made the point" if it's based on hand-waving and dubious generalities? I ask because you're trying to undermine why the Gates Foundation would look at dropouts as a metric — a point that you can't make with such a transparently flawed model. At best you can say that you've created an illusion of having made a point.