Peer assisted learning as a strategy that aims to facilitate the students’ development in intellectual, emotional, personal and social proportions. Based on social constructivist theory, the study employed mixed method approach- concurrent triangulation design. The study analyzed the use of peer assisted learning in enhancing academic achievement in secondary schools. It was conducted in Kisumu West Sub County due to a dropping in performance in Kenya National Examination. 34 principals, 366 teachers and 12,299 students made up the study population of 12,699. A Simple random sampling was used to sample 1 school. Purposive sampling was used to sample teachers and students. Purposive sampling was used to get form two class in the study. Data was collected by use of learners’ standardized achievement tests, questionnaires and interviews. In piloting, test retest method was employed to enhance the reliability of instruments for data collection. The qualitative data w as analyzed by organizing content into themes and sub themes. Quantitative data derived from questionnaire items was analyzed by use of descriptive statistics. Students were pretested through a standardized achievement test. On the basis of pre test results and the willingness of the students, a number of students were assigned to the experimental group treated through peer assisted learning and the rest were assigned to the control group. To determine the significance of the tutoring intervention a comparison of pre and post-test achievement of experimental and control groups, descriptive statistics of mean, median, standard deviation, coefficient of variation and analysis of covariance were used. The study results indicated that the experimental group showed greater improvement in their chemistry academic achievement as a result of their exposure to peer assisted learning strategy. Peer assisted learning had a visible effect on the posttest performance of the experiment group when tested at .05 level of significance. It was revealed that peer assisted learning was not embraced by teachers. Principals interviewed were aware that peer assisted learning was not used by teachers. The study recommended that peer assisted learning was useful a better strategy compared to other strategies.