Researchers on Wednesday cautioned against false hope. The findings suggest that the so-called autism spectrum contains a small but significant group who make big improvements in behavioral therapy for unknown, perhaps biological reasons, but that most children show much smaller gains. Doctors have no way to predict which children will do well.

Researchers have long known that between 1 and 20 percent of children given an autism diagnosis no longer qualify for one a few years or more later. They have suspected that in most cases the diagnosis was mistaken; the rate of autism diagnosis has ballooned over the past two decades, and some research suggests that it has been loosely applied.

The new study should put some of that skepticism to rest.

“This is the first solid science to address this question of possible recovery, and I think it has big implications,” said Sally Ozonoff of the MIND Institute at the University of California, Davis, who was not involved in the research.