A measurement of behavioral effectiveness in a longitudinal study of children in urban classrooms is presented. The specific nature of behavioral difficulties from kindergarten to third-grade, the stability of behavior patterns over this four year period, the relation between behavioral effectiveness and traditional measures of achievement success, and the use of behavioral effectiveness measures as a means of assessing program impact are discussed. Attention is focused on: (1) the degree to which children become more (or less) effective in coping with classroom demands, over their first four years of school, (2) correlates of effective behavior, (3) the degree to which prediction of later success might have been accomplished, and (4) the relevance of such data to programming for children. (Author)