In this analysis of 58 empirical studies of high school block scheduling, the authors report findings in and across five groupings. Within groups, data were inconsistent regarding whether teachers' practices changed, but teachers believed that staff development was necessary to teach in a block schedule. Block scheduling appeared to increase student grade point averages and improve school climate, but the results regarding its effects on standardized test scores and attendance were inconsistent. Across studies, the findings indicated that (a) research studies omit key information; (b) teachers and students may view block scheduling positively (but their reasons are unknown); and (c) changes in teachers' practices are inconsistent. Many studies reported data that were collected over short periods of time. The authors of this analysis offer generalizations about block scheduling research, recommendations for further research, and a discussion of implementation issues.