This study investigated the effectiveness and efficiency of the Reading Recovery early intervention. At-risk 1st-grade students were randomly assigned to receive the intervention during the 1st or 2nd half of the school year. High-average and low-average students from the same classrooms provided additional comparisons. Thirty-seven teachers from across the United States used a Web-based system to register participants (n = 148), received random assignment of the at-risk students from this system, and submitted complete data sets. Performance levels were measured at 3 points across the year on M. M. Clay's (1993a) observation survey tasks, 2 standardized reading measures, and 2 phonemic awareness measures. The intervention group showed significantly higher performance compared with the random control group and no differences compared with average groups. Further analyses explored the efficiency of Reading Recovery to identify children for early intervention service and subsequent long-term literacy support.