The purpose of this study was to adapt a methodology, which has previously been successfully employed in adult psychotherapy research, to study videotaped play therapy sessions with children. Therapist interventions in a child psychotherapy case were rated for Plan-compatibility, a case-specific measure of predicted helpfulness based on an independently generated case formulation. Independent judges rated patient material before and after each intervention with the Progressiveness Scale for Children, a generic measure of patient progress, and the Child Therapeutic Alliance Scale, an eight-item measure which assessed elements of the patient's working capacity. A significant association was found between the Plan-compatibility of therapist interventions and changes in patient behavior following the interventions on some items of the Child Therapeutic Alliance Scale and to a more modest extent, on the Progressiveness Scale for Children. This method shows some promise for use in assessing immediate changes in patient process in child psychotherapy.