[throwaway6579]

Throwaway, speaking from personal experience. I will note up front that none of what follows should be read as advocating a value judgement (I have certainly failed to conceal my own biases, regardless).

Lower middle and working class families lack the knowledge and financial resources necessary to obtain diagnoses, if they should feel it worthwhile. In working class families especially, autism and ADHD traits are either vilified as gross character defects or minimized as typical immaturity, with some variation with respect to gender role. In any case, diagnosis is less likely. In middle class families, where expectations of social function and independence are different, the same behaviors are treated very differently.