Depression may be key to some learning disabilities.

Studying tearning disabilities can be almost as frustrating as having to cope with one of them.

"A learning disability," says psychologist David Goldstein of Temple University in Philadelphia, "is...hard to define, but you know it when you see it." Estimates of the proportion of elementary school children with these academic problems range from 3 to 30 percent.

The causes of learning disabilities are also elusive, but in a five-year study Goldstein and co-workers have found that reading or arithmetic problems in a substantial number of learning-disabled children are primarily the result of depression.

"We're a long way from saying depression definitely causes academic failure," cautions Goldstein, "but we have a promising lead on a subgroup of children whose basic problem may be depression."

The term "learning disability" encompasses a variety of problems -- such as hyperactivity and an inability to read or understand arithmetic -- that result in failure in school. The children have normal or near-normal intelligence.

This broad definition, says psychologist Judith M. Rumsey of the National Institute of Mental Health, describes only what the children are not doing -- learning well in school. The trick is to find subgroups of children with specific strengths and weaknesses.

Goldstein says there is a subgroup -- about one-third of 159 learning-disabled children he studied -- in which emotional disorders appear to lead to academic failure. For the rest, he adds, depression is often the consequence of learning failures that may be caused by neurological problems.

His sample was screened from 300 children tagged by Philadelphia-area teachers as learning-disabled. The youngsters, whose average age was 9 years at the start of the project, were given a battery of depression tests annually. The researchers were looking for evidence of poor interpersonal relationships, inappropriate behavior or feelings, a pervasive mood of unhappiness and psychosomatic complaints.

All of the children were more depressed than previously tested samples of non-learning-disabled students, but depression appeared to account for disabilities in 50 cases. Depression scores for these children remained stable over time, while the same scores for the larger subgroup fluctuated. This indicates, says Goldstein, that children in the latter group reacted to periodic family problems or to other events. Depression and academic achievement were related only in the group with consistent levels of depression. Children identified as having depression as a cause of school failures improved markedly in reading and math over the study period after receiving special instruction in small classes and two hours of individual therapy per week.

Goldstein's contention that some learning disabilities are a result of depression is still open to interpretation, says Rumsey. Many researchers assume that the basis of learning problems is primarily biological, she notes. Some stress deficits in the brain's left hemisphere, which controls speech and language; others emphasize deficits in the right hemisphere, which regulates visual and motor skills.

But it is difficult to measure neurological problems in many learning-disabled children, says psychologist Lynne Feagans of the University of North Carolina in Chapel Hill. She and her colleagues have targeted 13 learning-disabled subgroups based on language and behavior problems. "It surprises me," she says, "that so many kids had a primary depression in Goldstein's study. But can you really say which comes first, depression or school problems?"

Responds Goldstein: "It's important to recognize the role that emotional disturbances play so that appropriate treatment can be given."