The study reviewed in this paper examined three separate methods for teaching the "control of variables strategy" ("CVS"), a procedure for conducting a science experiment so that only one variable is tested and all others are held constant, or "controlled." The study analyzed data from a randomized controlled trial of 848 fourth-grade students in 39 classrooms in 12 schools in Fayette County, Kentucky. Classrooms with similar achievement levels (within schools, when possible) were formed into triplets. Within each triplet, classrooms were randomly assigned to one of three conditions: (1) "Instruct": Teachers taught "CVS" in an interactive lecture format; (2) "Manipulate": Teachers taught "CVS" by providing time for students to design and run experiments in groups; or (3) "Both": Teachers taught "CVS" through both interactive lectures and by providing time for experimentation in groups. The study assessed the impact of each of the three strategies by testing student understanding of the concepts at three points: the day before instruction, the day after instruction, and five months after instruction. The study found, and the What Works Clearinghouse (WWC) confirmed, statistically significant differences in student performance on the "CVS comparison assessment" at posttest among the three conditions. Students in the "Both" condition outperformed students in the "Manipulate" condition and the "Instruct" condition, and students in the "Instruct" condition outperformed students in the "Manipulate" condition. In addition, students in the "Both" condition outperformed students in the "Manipulate" condition on the "ramps test." These findings indicate that using a combination of interactive lectures and manipulative experiments was the most effective method of teaching "CVS." The research described in this report meets WWC evidence standards without reservations. Appended are: (1) Study details; (2) Outcome measures for each domain; (3) Study findings for science achievement; and (4) Supplemental findings by achievement level. A glossary of terms is included. (Contains 2 endnotes.) [The following study is the focus of this review: "Learning the Control of Variables Strategy in Higher and Lower Achieving Classrooms: Contributions of Explicit Instruction and Experimentation" (EJ876300).]