Data were collected in a longitudinal study of 134 boys and 132 girls and their families during kindergarten and first grade. Four hours of parent-child interaction were coded to ascertain parent discipline practices. A structured interview assessed maternal attributions about child behavior. Maternal ratings of child conduct problems at kindergarten entry reliably predicted the mother's subsequent hostile attributions concerning child misbehavior and use of ineffective discipline tactics. Ineffective maternal discipline and the interaction of ineffective discipline and hostile attribution predicted growth in child conduct problems at home during kindergarten and first grade. Changes in teacher-reported and observed child conduct problems at school during kindergarten and first grade were predicted by growth in conduct problems at home and by the interaction of ineffective discipline and hostile attribution.