This study examined the effects of a constructivist mathematics intervention for students with mild mental retardation, as compared to direct instruction, which is often recommended for these children. A total of 69 students from elementary schools for special education participated in the study, which focused on multiplication learning. They received one of two kinds of mathematics intervention, guided or directed instruction. Multiplication automaticity and ability tests were administered before and after the four-month training period. The results show that students in both conditions improved significantly during the training period. However, students who received directed instruction showed greater improvement than students who had received guided instruction. These results show that students with MMR can profit from constructivist instruction, although direct instruction seems more effective.