This study evaluated an approach to professional development for middle school science teachers by closely examining one grade 8 course that embodies that approach. Using a cluster-randomized experimental design, the study tested the effectiveness of the Making Sense of SCIENCE[TM] professional development course on force and motion (Daehler, Shinohara, and Folsom 2011) by comparing outcomes for students of teachers who took the course with outcomes for students of control group of teachers who received only the typical professional development offered in their schools and districts. The study estimated impacts on student science achievement for all grade 8 students in the study sample as well as for the subsample of English language learners. It also estimated impacts on teacher science and pedagogical knowledge. Results for the primary confirmatory analyses indicate that after adjusting for multiple comparisons, there were no statistically significant differences between the test results on science content of students in intervention group classrooms and students in control group classrooms. Intervention group students in neither the full sample (effect size = 0.11) nor the English language learner subsample (effect size = 0.31) scored significantly higher on the ATLAST Test of Force and Motion than did their control group counterparts. Similarly, intervention group students in neither the full sample (effect size = 0.03) nor the English language learner subsample (effect size =0 .09) scored higher on the physical science reporting clusters of the California Standards Test than did their control group counterparts. Results for the intermediate confirmatory analyses indicate that after adjusting for multiple comparisons, teachers who received the professional development course outscored their control group counterparts on the ATLAST Test of Force and Motion for Teachers (effect size = 0.38), as well as on their ratings of confidence in their ability to teach force and motion (effect size = 0.49). With one exception, the study findings were not sensitive to variations in specification of the estimation models. The exception is that, for teacher content knowledge, inclusion of the pretest in the impact analysis model (basic model plus pretest) decreased the point estimate from 9.8 to 6.1 and the effect size from 0.61 to 0.38. In exploratory analyses, the study investigated whether there were differential impacts on student and teacher content knowledge outcomes across the six research sites. The estimated impacts were most pronounced at two of the six sites. For the full sample of students, point estimates for student and teacher content knowledge of force and motion followed exactly the same rank order at all sites. There are three main limitations of this study. First, there was high sample attrition: 48 of the 181 teachers who were randomly assigned to intervention and control groups left the study before data collection was completed. However, there is no evidence that attrition resulted in significant differences at the baseline between the intervention and control samples used in the analysis. Second, the study did not include analyses of classroom implementation of course-related practices. As a result it is not possible to infer whether the lack of student effects is due to a failure of treatment group teachers to modify classroom practices or a failure of modified practices to affect student outcomes. Third, the findings are based on volunteer teachers and students whose parents provided consent. It is possible that the findings would have been different had teachers been required to participate in the intervention, and all students been tested. Appended are: (1) Study power estimates; (2) Procedure for assigning blocks for recruited sample and final analytic sample; (3) Teacher agreement to protect the study; (4) Teacher survey responses related to contamination across groups; (5) Parent consent form; (6) California content standards in physical science reporting clusters; (7) Student data obtained from district administrative records; (8) Survey items used to measure teacher confidence; (9) Course session video recording protocol; (10) Course session attendance sheet; (11) Student test administration instructions for proctors; (12) Teacher test administration instructions for site coordinators; (13) Baseline equivalence of teacher demographics in intervention and control group samples; (14) Class selection worksheet; (15) Sensitivity analysis for nesting of students within teachers or classes within teachers; (16) Impact estimation methods; (17) Missing item--level data; (18) Schedule and content goals of Making Sense of SCIENCE[TM] professional development course on force and motion; and (19) Sensitivity analyses based on different models and analytic samples. (Contains 51 tables, 4 figures and 8 footnotes.)