This research evaluates effectiveness of Canadian social workers as mediators of problems between children and their families. The research is based on investigation of 118 social workers in centers for aid for children in Ottawa and Montreal. Seven chapters comprise the document. Chapter I summarizes the origins and phases of the study, and basic research concerns including social worker effectiveness, the role of the social worker, the interdependence of behaviors of the social worker, and the interdependence of the worker, the client, and social variables. Chapter II provides the framework of the study, explains the theory of mediation, analyzes the interaction between social worker and client, and discusses formation of the Questionnaire on the Behavior of Social Workers. Chapter III defines social worker effectiveness and discusses the Questionnaire on Client Satisfaction and documentation from agency files. Chapter IV discusses the participating agencies and social workers, the method of compiling results, the sample, the excluded group (non-respondents), and variables concerning the social worker. Chapter V presents a model for the study of social service and provides an overview of the behaviors of the social worker and influences of these behaviors. Chapter VI outlines profiles of behaviors and effectiveness of social workers according to educational background and work experience. Chapter VII discusses limitations of the study, summarizes conclusions, and suggests future research topics. The questionnaires, tables of responses, and a model for mediation are included in appendices. (KC)