Noting that multiage classes during the elementary school years have been an option of educational practice in the United States since the introduction of graded education in the 19th century, this digest discusses the research on multiage education and its impact on academic achievement. Despite inconsistencies in research findings, those studies that report significant achievement outcomes for students in multiage classrooms over those in single-age classes demonstrate gains in language (including vocabulary and literacy measures) and mathematics. The key to interpreting research outcomes may be how multiage is defined. The digest points out that the academic benefits demonstrated for students in multiage classrooms may be the result of the classroom teacher's active facilitation and encouragement of cross-age learning opportunities. Widespread acceptance of the multiage model in elementary schools is unlikely until it is clear that multiage education leads to greater academic achievement. If careful attention is given to definition and selection of multiage classrooms, and detailed descriptions of classroom procedures are provided, research outcomes may reliably indicate which specific aspects of multiage classroom practices are most beneficial. (Contains 16 references.) (HTH)