This article presents a systematic review of research on the achievement outcomes of all types of approaches to teaching science in elementary schools. Study inclusion criteria included use of randomized or matched control groups, a study duration of at least 4 weeks, and use of achievement measures independent of the experimental treatment. A total of 17 studies met these criteria. Among studies evaluating inquiry-based teaching approaches, programs that used science kits did not show positive outcomes on science achievement measures (weighted ES=+0.02 in 4 studies), but inquiry-based programs that emphasized professional development but not kits did show positive outcomes (weighted ES=+0.30 in 8 studies). Technology approaches integrating video and computer resources with teaching and cooperative learning showed promise (ES=+0.37 in 5 studies). The review concludes that science teaching methods focused on enhancing teachers' classroom instruction throughout the year, such as cooperative learning and science-reading integration, as well as approaches that give teachers technology tools to enhance instruction, have significant potential to improve science learning. (Contains 3 tables.) [For "Effective Programs for Elementary Science: A Best-Evidence Synthesis. Educator's Summary," see ED539696.]