This study investigates the efficacy of an integrated science and literacy approach at the upper-elementary level. Teachers in 94 fourth grade classrooms in one Southern state participated. Half of the teachers taught the treatment unit, an integrated science-literacy unit on light and energy designed using a curriculum model that engages students in reading text, writing notes and reports, conducting firsthand investigations, and frequent discussion of key concepts and processes to acquire inquiry skills and knowledge about science concepts, while the other half of the teachers taught a content-comparable science-only unit on light and energy (using materials provided by their districts) and provided their regular literacy instruction. Students in the treatment group made significantly greater gains on measures of science understanding, science vocabulary, and science writing. Students in both groups made comparable gains in science reading comprehension. (Contains 10 tables and 9 notes.)