In the study, researchers analyzed mental disability in 53,622 youngsters aged 6 to 17, based on ratings provided by parents. The parents scored their children on a so-called impairment scale.

The scale asks, for instance, how much of a problem a child has with “Feeling unhappy or sad?” “Having fun?” “Getting along with other kids?” “Feeling nervous or afraid?” The scale had 13 items in all, and parents assigned each one a “0,” for no problem, up to “4,” for a “very big problem.” Children whose scores were 16 or higher qualified as severely impaired. The data was drawn from in-depth household surveys performed by the Agency for Healthcare Research and Quality.

Between 1996 and 2012, the percentage of children and teenagers in that severe category dropped to 10.7 percent from 12.8 percent. That is a 16 percent decrease, and it was entirely unexpected, said Dr. Mark Olfson, of Columbia University, the study’s lead author. “The finding is robust and real and challenges the prevailing stereotype that young people are somehow more vulnerable to mental problems,” said Dr. Olfson. His co-authors were Dr. Benjamin Druss of Emory University and Dr. Steven Marcus, of the University of Pennsylvania.

In contrast to the new study, many government surveys have suggested that there were increases in the prevalence of serious mental disorders among children and teenagers.

One recent survey reported that rates of attention deficit disorder, the most common childhood mental health problem, rose to 10 percent from 7 percent between 2003 and 2010 and suggested an underlying rise in prevalence. Another report that came out in 2013 estimated that 13 percent to 20 percent of young people had mental disorders considered “serious deviations from cognitive, social and emotional development.” It concluded that prevalence of these conditions was increasing. And prevalence estimates for autism spectrum disorders increased to one in 88 from one in 110 from 2006 to 2008.

Dr. Olfson said that his study did not investigate why the prevalence of severe problems might have changed. Yet several explanations are plausible, he said. One is that the current generation of parents is doing something right, despite lingering worries about “helicopter parenting,” permissiveness, and video games. Another is that children with severe problems are increasingly likely to get psychiatric care earlier.

The new study found that the overall rate of young people being treated for a mental disorder increased, to 13 percent from 9 percent. But the steepest increases in use of mental health services were among the most impaired — to 44 percent in 2012 from 26 percent in 1996.