Significant correlations were found between grades for reading, writing, and calculating and each child's individual mean reaction time for symbolic motor performance tasks with letters and numbers as stimuli for 240 elementary school boys with minimal brain dysfunction and in first to fourth classes in Prague (Czechoslovakia) and Skopje (Yugoslavia). For age(class)-matched groups of 382 healthy boys the correlations disappeared by the age of ten years. Similar results were noted for groups of boys in both cities.