With the increase of federal funds for education, a new professional is emerging--the "evaluator"--whose role needs to be more clearly defined. He must not, first of all, take an absolutist position in his relationship to other educational experts or he will fail to get the cooperation of teachers and the support of powerful community groups. Second, he must accept certain basic assumptions with regard to educational goals: (1) educational goals should be defined in a process of interaction between professionals and representatives of the society, (2) goals and practices must be varied to accommodate a diverse population and must change as needs and values change, (3) goals must not be limited to purely academic objectives, and they must be stated in descriptive rather than interpretive language. The function of the professional evaluator should be to help teachers and administrators in a given school (1) to define their goals in terms of pupil performance, (2) to learn how systematically to discover differences among pupils that require particular kinds of instruction, and (3) to design and administer evaluation programs in order to find out which of their instructional procedures are paying off and which are not. It is hoped that the research and development evaluator will bridge the gap between the laboratory and the field by making explicit to the individual teacher the relevance of research findings to his work. (JS)