This study evaluated the effectiveness of two promising interventions – computerized attention training and computer-assisted instruction (CAI) – for 77 first-graders identified by their teachers as having attention difficulties. Project CLASS assessed the impact of these interventions on students’ behavior, attention and academic achievement. Students who received either intervention were more likely than controls to show a moderate decline in teacher-rated attention problems during first grade, and students in the CAI group were more likely to show gains in teachers’ ratings of their academic skill level and productivity. Gains in academic achievement for intervention students were not evident, however, and differences between intervention and control participants had dissipated by midway through second grade. This was largely attributable to a general decline in attention problems over time. Attention difficulties were associated with lower reading achievement in first, but not second, grade, while the opposite pattern was suggested for math. Attention problems that persisted into second grade were associated with compromised academic performance in multiple domains. Overall, results suggested that attention difficulties exert an adverse affect on children’s early academic achievement and that the interventions tested in this study did not have a sufficiently robust impact to promote better academic outcomes.