Large numbers of U.S. students lack proficiency in science, and students from different racial/ethnic and socioeconomic groups show disparities in science achievement. Science knowledge and skills are important for both academic and workplace success, and a variety of interventions have been developed to improve student achievement in science. These interventions include professional development programs for teachers that are designed to change teachers' content knowledge or classroom instruction in science. "Science Teachers Learning through Lesson Analysis" ("STeLLA"®) is a professional development program, developed by BSCS Science Learning, that aims to improve students' science achievement by improving teachers' science content knowledge and their abilities to: (1) explain science concepts to students; (2) clearly identify to students the science concepts used in student learning activities; and (3) engage students in thinking about science. This What Works Clearinghouse (WWC) intervention report, part of the WWC's Primary Science topic area, explores the effects of "STeLLA"® on science achievement. The WWC identified three studies of "STeLLA"®. One of these studies meets WWC standards. The evidence presented in this report is from one study of the effects of "STeLLA"® on students--including 59% White, 4% Black, 2% Asian, and 28% Hispanic students--in grades 4 and 5 in urban, suburban, and rural schools in Colorado. [For the Intervention Brief, see ED612712. For the Intervention Snapshot, see ED612713.]