Comparing children in some new study against the general population of mainstream children is the general approach we use and it's fraught with problems. The s

Comparing children in some new study against the general population of mainstream children is the general approach we use and it's fraught with problems. The studies are often small sample sizes of children who are often opted-in by their parents and the teaching is done by better than average teachers with lots of support and involvement from the institution who designed the study or otherwise stands to gain from its successful outcome. All that is generally revealed is that children whose parents are engaged in their education being taught by good teachers and that are aware they are in a 'special' group do better than average. Unsurprisingly the methods don't scale very well.