This study evaluates the effectiveness of Computer-Assisted Instruction (CAI) compared with traditional classroom instruction of mathematics of seventh graders in Kuwait's public schools. We aimed to compare students learning outcomes between two groups: the control group, taught traditionally without the use of computers, and the experimental group, receiving CAI supported instruction in the same grade level. We examined the difference in learning outcomes and attitudes towards mathematics between the CAI and traditional instruction groups. This quasi-experimental research followed the pre-test/post-test equivalent group design. The CAI group used a combination of discovery-environment and simulation software supported by the Cambridge HOTmaths environment. Results indicate that total gain in mathematics achievement from CAI is statistically significantly higher than with traditional teaching methods. CAI was more effective in increasing students' mathematical comprehension and application skills in the experimental group. Components related to the development of total attitude towards each of mathematics enjoyment, mathematics values, mathematics learning, and attitude towards mathematics favored the experimental group. Overall, the significance tests supported our hypotheses that CAI could contribute effectively to teaching methods; made it possible to improve students' mathematics achievement and increase positive attitude towards the subject.