Researchers and evaluators have been attempting to document the impact of ubiquitous or 1:1 computing on students, teachers, schools, and communities. However, the most recent reviews of research on 1:1 computing initiatives reflect a dearth of rigorous studies and emphasize the need for well-designed, scientifically based research to measure the impact of 1:1 learning on student achievement. This study investigates the effect of 1:1 laptop to student ratios on math and science achievement in at-risk middle school students. The researchers used a pretest-posttest control-group design. The findings are based on between-groups analysis of covariance (ANCOVA) of longitudinal data comparing standardized achievement test scores. The researchers compared the test scores of students randomly assigned to 1:1 laptop classrooms with the test scores of students in classrooms without 1:1 laptops in the same middle school. Students were exposed to the treatment for two years and the authors used the students as the unit of analysis. Pre-existing achievement scores for each student were included as a covariate to statistically equate groups previous to analysis. Results showed significant post-intervention program effects for science achievement. Furthermore, there was a gender effect in science achievement, with boys significantly outperforming girls in the same 1:1 laptop classroom. In contrast, no significant program effects for math achievement were obtained. The results suggest that 1:1 laptop instruction can increase student achievement under certain conditions. This study has implications for policymakers, instructional designers, and educators who are currently implementing a 1:1 laptop program or considering such an implementation. The authors suggest the need for further research to help determine the efficacy of 1:1 laptop instruction and the implementation conditions necessary for increased student achievement in this context.