Sir.—The concern Dr. and Ms. Lerer show over the 38% incidence of learning-disabled children in our sample arises from the assumption that the sample was randomly selected. The "18 research classrooms" referred to in our article were each composed of approximately 50% learning-disabled and 50% randomly selected students, with the former previously identified for placement by screening instruments. We believed it necessary to more precisely define the learning-disabled group in order to strengthen the validity of our findings. Using the stringent criteria outlined in the article, the incidence of learning-disabled children in our districts is estimated at 7% to 8%.
Further points allude to nonhyperkinetic children with short attention spans. We would concur that such children should be referred for medical examination (and consideration for medication, whether soft signs are present or absent).
We will be interested to learn the outcome of the Lerers' study, suggesting a correlation