Yet now some powerful figures in mental health are claiming to have identified a new disorder that could vastly expand the ranks of young people treated for attention problems. Called sluggish cognitive tempo, the condition is said to be characterized by lethargy, daydreaming and slow mental processing. By some researchers’ estimates, it is present in perhaps two million children.

Experts pushing for more research into sluggish cognitive tempo say it is gaining momentum toward recognition as a legitimate disorder — and, as such, a candidate for pharmacological treatment. Some of the condition’s researchers have helped Eli Lilly investigate how its flagship A.D.H.D. drug might treat it.

The Journal of Abnormal Child Psychology devoted 136 pages of its January issue to papers describing the illness, with the lead paper claiming that the question of its existence “seems to be laid to rest as of this issue.” The psychologist Russell Barkley of the Medical University of South Carolina, for 30 years one of A.D.H.D.’s most influential and visible proponents, has claimed in research papers and lectures that sluggish cognitive tempo “has become the new attention disorder.”