The study examined the Impact of Peer-Mediated Learning on achievement and motivation in computer science among senior secondary school students in Minna metropolis, Niger state. The study adopted a randomized pre-test, post-test control group design. Two hypotheses were formulated to guide the study. Purposive sampling technique was used to select four (4) Private Secondary Schools from Minna, Metropolis. Eighty (80) Students were drawn from the four Secondary Schools as sample size through stratified random sampling technique. Validated Test Instrument; Basic Computer Skills Acquisition Test (BCSAT) and Questionnaire: Motivated Strategy for Learning Questionnaire (MSLQ) vetted by experts from Computer Science and Educational Technology Departments were used for data collection. The BCSAT was made up of 20 items multiple-choice objective test questions to test students' cognitive knowledge and 5 practical questions, each comprising steps that tested students' computer practical skills while MSLQ, a Likert scale with 31 items was used to determine the motivational beliefs of students taught computer skills. ANOVA and Kruskal Wallis H test was used for data analysis and was tested at 0.05 level of significance. The study revealed that there was a statistically significant difference in the mean scores of students taught using Peer-Mediated Learning (PML) than those taught using conventional method. The study further revealed that students' motivation towards PML were significantly positive when compared to the students taught using conventional method. Based on these findings, the researchers recommended that Secondary Schools should adopt PML for effective teaching and learning of computer skills related concepts in Computer Science.