Understanding ADHD neurological research

Many respond to the research in the article below as if it shows that biological deficits give rise to ADHD behavior. However, the findings only show a correlation between children who respond with ADHD behaviors and certain kinds of biological patterns. We might just as readily assume that doing ADHD behavior over time changes biological development just like what happens to muscle development when people don't exercise.   http://blogs.edweek.org/edweek/inside-school-research/2011/02/studies_point_to_new_way_to_id.html