The purpose of this research study was to investigate the role of manipulative materials in improving achievement in computation, concept-formation, and problem-solving in fourth-grade mathematics. This study examined whether manipulative materials had greater impact when used to introduce a concept, to reinforce a concept, or both to introduce and to reinforce a concept. The sample group for this study was 123 students. The children in experimental Group A (n=41) used manipulative materials for the first lesson in a concept. Experimental Group B (n=27) used manipulative materials only after initial instruction on the concept by the traditional method (lecture by teacher using blackboard and textbook). Experimental Group C (n=28) used manipulative materials for initial instruction, practiced the concept using the textbook, and reinforced the concept through additional use of manipulatives. All experimental groups continued to use the adopted text as well as the manipulatives. Control Group D (n=27) used only the textbook and had no lessons involving manipulative materials. The Science Resource Associates (SRA) Achievement Tests, Level E, Form 2, and researcher-designed achievement and retention tests were administered to the subjects. Data from the posttests were analyzed using an analysis of covariance model with multiple contrasts. The analysis of scores on the SRA tests showed no significant difference between groups on the concepts and computation tests. Group A, which used manipulative materials for introduction, scored significantly higher than the other groups on the problem-solving test (p=.05). The analysis of scores on the researcher-designed tests indicated a significant difference between groups on both the achievement and retention tests. Both Group A, which used manipulatives for the introduction of concepts, and Group B, which used manipulatives for reinforcement, scored significantly higher than the other groups on both researcher-designed tests. / Ed. D.