Abstract
<title>Abstract</title> <p>The mole concept is a key subject in chemistry, which helps students grasp the quantitative aspects of chemical reactions. Nevertheless, the mathematical and abstract nature of the concept makes it very challenging for many secondary school students, causing poor performance and negative attitude towards the study of chemistry. This research looks at peer tutoring as a strategy of cooperative and learner-centered instruction that aims to improve the performance of senior two learners in the topic of mole. A quasi-experimental research design with experimental and control groups, guided by the social constructivist theory of Vygotsky guide this study. Six public and government-aided secondary schools from Rulindo district with a sample size of 368 students obtained using Yamane’s formula participated in the study. Data was collected using a mole concept achievement test questionnaire administered before and after the intervention where in the experimental group taught using peer tutoring strategy in the control group students were taught using existing teaching approaches. The findings showed that peer tutoring significantly enhanced the performance of students of the mole concept. Descriptive and inferential statistical analysis was done on the quantitative data obtained through calculating means, standard deviations and performing t-test. An independent samples t-test found that the experimental group scored significantly higher on the post-test [M = 30.55, SD = 8.78] compared to the control group [M = 24.05, SD = 10.98, t (182) = -6.255, p < .001]. The results suggest that peer tutoring was more effective compared to existing teaching methods. This study has shown that peer tutoring is helpful in implementing the competence-based curriculum in Rwanda. It is suggested that chemistry teachers should consider this approach to help their students improve in the mole concept.</p>