This study investigated whether there were differences in science teachers' efficacy, perceptions of support and knowledge of developmentally appropriate curriculum and instruction in the two organizationally different settings of the junior high and the middle school. Teacher questionnaires were used as a source of data. From 127 returned questionnaires from teachers (a response rate of 79.4%) several conclusions were drawn. Among them were that: (1) the level of professional teaching efficacy was significantly higher for middle school science teachers than it was for junior high science teachers; (2) as compared to the junior high school teachers, science teachers in the middle schools had a greater understanding of the curriculum and instructional strategies that are most appropriate for adolescent students; (3) school organization, certification type, perceptions of support, and knowledge of developmentally appropriate curriculum and instruction are negligible predictors (5%) of personal efficacy; and (4) when type of school organization and type of certification are controlled for, knowledge of developmentally appropriate curriculum and instruction was the best predictor of professional science teaching efficacy for both middle and junior high school science teachers with secondary certification and for middle school science teachers with elementary certification. (PR)