Although research on Tier 2 interventions for early mathematics is accumulating, such efforts remain far behind those for reading, especially regarding specific features such as the ideal time to begin an intervention. The present study investigated the effectiveness of a Tier 2 intervention using a single subject multiple baseline, across-groups design with two cohorts of second graders. Because the two cohorts of students were given the intervention at different times during the second grade year, the study also documented whether the timing of the intervention affected acquisition and retention of second grade mathematics competencies. Finally, the study tracked student performance up to the first semester of the third grade year to document any sustained effects. The results show that the supplemental intervention was effective for both cohorts, but differences in performance indicate that the timing of the intervention may affect the degree of success. In addition, for some participants, the positive effects of the intervention were sustained into the third grade year.