Computer-Assisted Instruction (CAI) offers the potential to deliver cognitive and meta-cognitive strategies in mathematical word problem-solving for students with mathematics difficulties. However, there is a lack of commercially available CAI programs with cognitive and meta-cognitive strategies for mathematical word problemsolving that pay particular attention to the critical design features for students with mathematics difficulties. Therefore, empirical evidence regarding the effects of CAI program with cognitive and meta-cognitive strategies on the word problem-solving of students with mathematics difficulties has not been found. Considering the imperative need for a CAI program with cognitive and metacognitive strategies for students with mathematics difficulties, an interactive multimedia software, 'Math Explorer, ' was designed, developed, and implemented to teach one-step addition and subtraction word problem-solving skills to students with mathematics difficulties. Math Explorer incorporates: (a) four-step cognitive strategies and corresponding three-step meta-cognitive strategies adapted from the research on cognitive and meta-cognitive strategies, and (b) instruction, interface, and interaction design features of CAI identified as crucial for successful delivery of cognitive and metacognitive strategies for students with mathematics difficulties. The purpose of this study was to investigate the effectiveness of Math Explorer, which was designed to be a potential tool to deliver cognitive and meta-cognitive strategy instruction in one-step addition and subtraction word problem-solving. Three research questions guided this study: (a) To what extent does the use of Math Explorer affect the accuracy performance of students with mathematics difficulties in grades 2-3 on computer-based tasks with one-step addition and subtraction word problem-solving?, (b) To what extent does the use of Math Explorer generalize to the accuracy performance of students with mathematics difficulties in grades 2-3 on paper/pencil-based tasks with one-step addition and subtraction word problem-solving?, and (c) To what extent does the use of Math Explorer maintain the accuracy performance of students with mathematics difficulties in grades 2-3 on computer- and paper/pencilbased tasks with one-step addition and subtraction word problem-solving? A multiple probe across subjects design was used for the study. Four students with mathematics difficulties participated in the pre-experimental (i.e., introduction; screening test; and computer training I) and experimental (i.e., baseline, computer training II, intervention, and follow-up) sessions over an 18-week period. Each week of the intervention phase, the students received an individual 20- to 30-minute Math Explorer intervention, at most, five days. After each intervention, they took the 10-minute computer- or paper/pencil-based tests developed by the researcher. The intervention phase for each student lasted five to seven weeks. Two weeks after termination of the intervention phase, their accuracy performance on the computer- and paper/pencil-based tests were examined during the follow-up phases. The findings of the study revealed that all four of the students were able to use the cognitive and meta-cognitive strategies to solve the addition and subtraction word problems and improved their accuracy performance on the computer-based tests. Their improved accuracy performance found on the computer-based tests was successfully transferred to the paper/pencil-based tests. About two weeks after termination of the intervention phase, except for one student who had many absences and behavioral problems during the extended intervention phase, the three students successfully maintained their improved accuracy performance during the follow-up phase. Taken together, the findings of the study clearly provide evidence that Math Explorer is an effective method for teaching one-step addition and subtraction word problem-solving skills to students with mathematics difficulties and suggest that the instruction, interface, and interaction design features of CAI program is carefully designed to produce successful mathematical performance of students with mathematics difficulties. Limitations of the research and implications for practice and future research were discussed.