This paper describes one aspect of a multi-factor investigation of the parameters which mediate in the effectiveness of an inservice staff development program. The paper also represents an attempt to recognize and to meet the problems associated with the evaluation of inservice programs for teachers in terms of student outcomes. The inservice course consisted of a two year program used to introduce methods of Cognitive Acceleration through Science Education (CASE) in 13 schools, between September 1991 and July 1993. CASE is a two year intervention program used in grades 6 and 7 whose objective is the promotion of formal operational thinking. Measures made in the study include assessments of the level of use of CASE by the teachers, and measures of cognitive gains by the students. A strong relationship was demonstrated between the level of use of the CASE intervention methods, as reported by teachers, and the cognitive gains made by their pupils. It is claimed that this finding represents both a substantial confirmation of the effectiveness of the CASE inservice program, and a demonstration of how a staff development program may successfully be evaluated using a process-product design. Contains 18 references. (LZ)