Dr. Rachel Klein has been following a group of some 200 boys with ADHD for more than 30 years. I should say boys with the symptoms of what we now call ADHD, because the diagnosis didn’t exist in 1970 when she and her colleagues began the study. The boys were around 8 at the start, of average or higher intelligence, and hyperactive and inattentive both at home and at school. Those who exhibited aggressive or anti-social behavior, which we’d now call conduct disorder, were not chosen for the study, to keep it focused on the outcomes of ADHD alone. They were compared to a control group of kids who were described by teachers and parents as behaving typically.

It’s a remarkable study because of the detailed interviews and data collected from these children well into adulthood. The boys were interviewed again when they were 18, 25 and 41. Dr. Klein, who is director of the Anita Saltz Institute for Anxiety and Mood Disorders at the NYU Child Study Center, reviewed the findings during a visit to the Child Mind Institute Friday.

The kids with ADHD overall fared worse in school, in jobs, in family stability, and with the law, than the control group. But one of the one of the key findings is that 60 percent no longer qualified for an ADHD diagnosis at 18—and those kids who outgrew their symptoms fared differently over the long term than kids whose ADHD symptoms persisted.

Of the kids in the original ADHD group, the 40 percent who still qualified for the diagnosis at 18 were much more likely to have developed two new problems during adolescence—anti-social personality disorder and substance abuse disorders—than those who had outgrown their ADHD, or the control group. And they were most likely to develop them in the same order, in what Dr. Klein called a “developmental cascade”: ADHD heightens risk for anti-social personality disorder, which in turn heightens risk for substance-abuse disorder.

But the good news is that the interviews at 25 and then 41 showed no heightened risk for new anti-social or substance abuse disorders after the checkup at 18. There are still clear disadvantages that continue into adulthood for the group in which the ADHD persists-but they all started in adolescence. As Dr. Klein put it, “If you’ve made it through adolescence, you’ve made it, relatively speaking.”