This paper examine the effects of computer-assisted instruction (CAI) on the academic achievement of Nigerian students, using Junior Secondary School (JSS) graders from two secondary schools in Calabar Municipality, Cross River State, as study area. Four null hypotheses were formulated based on the major variables of teaching methods, motivation gender and attitude towards the subject; and tested with the dependent, and independent t-test statistics. A pre-test - post-test design was used to compare the experimental and control groups in which 100 respondents were randomly selected from JSS-II from the two sampled schools and subjected to 6-weeks of treatment effects. The result showed that experimental subjects have superior mathematics performance ability than those of the control group. That males and females do not differ significantly in their performance in computer-assisted learning in the experimental group; but boys in the control group differ significantly, with the boys outperforming the girls in the subject. In respect of attitude of students towards the subject, it was found that the experimental group does not differ in their attitude towards mathematics nor computer learning instruction. It was recommended among others that mathematics curricula be redesigned to integrate everyday household curriculum issues such as using culturally relevant institutional materials aids as well as use of certain cultural plays by children such as the Chimpanzee's Puzzle game.