The purpose of this study was to measure the effect of the Baylor College of Medicine Summer Science Institute (BCMSSI) on teacher science content knowledge and students' science performance. The analysis of the effect of participation showed an increase of 253 scale score points on the 2015 State of Texas Assessments of Academic Readiness, (STAAR) science performance of eighth grade students whose teachers completed all 60 professional development (PD) hours. A higher proportion of 5th - and 8th-grade students whose teachers completed the full PD hours met Satisfactory at the Level II phase-in 1 standard and Advanced performance standard on the 2015 STAAR science test compared to their peers whose teachers did not complete the full PD hours. The results also showed statistically significant moderate to large gains in teacher content knowledge and self-efficacy at all grade levels. Teachers at all grade levels were also, overwhelmingly, positive about the science institute and agreed that the resources and materials that they received were useful. Increasing the number of teachers who complete the BCMSSI program should be considered. Continued instructional focus should be placed on improving the science performance of at-risk and economically disadvantaged students. [For the 2013-2014 report, see ED599251.]