The purpose of this paper was to examine the effect of instructional supervision on teacher’s competences in Public Primary School in Rwanda. More specifically this researcher paper analyzed the preparation of teaching and learning documents and assessment practices. In this study 6 head teachers and 148 primary teachers from three selected sectors of Kamonyi district was related as informants. For selecting the sample size, the researcher adopted the two techniques that were purposive and simple random sampling techniques. The researcher was managed to use questionnaire, interview guide plus observation protocols aimed at combining primary and secondary data. To analyze the quantitative and qualitative data descriptive statistics was used in terms of mean, while in terms of statistics correlation and regression the researcher was used standard deviation and inferential. The findings were organized around the research objective and informed that most of head teachers conduct instructional supervision every day to help teachers to develop their competences. Most of teachers agreed that instructional supervision play a great role on the preparation of pedagogical documents where 78.9% agreed on this point. 81.07% agreed that instructional supervision influence assessments practices. It was revealed that instructional supervision influence teachers’ competences as shown by high positive correlation of 0.821. Further results showed that a one percent (1%) change in classroom visits will lead to 0.488% variation in teachers’ competence; also, a one percent (1%) change in provision of instructional resources practice will lead to 0.269% variation in teachers’ competence. Further, a one percent (1%) change in checking teachers’ records will lead to 0.384% variation in teachers’ competence and lastly a one percent (1%) changes in providing teachers’ assistance and feedback after observation will lead to 0.221% variation in teachers’ competence. As recommendation, primary school leaders should know that instructional supervision is very important and needs to be a priority in schools and given enough time so that improvement in education can occur. Next, school rules should plan the supervisory practices in normal way as long as beginner and expert teachers have the option of selecting from a variety of teaching styles. Last, the researchers are advised to carry out more studies in order to discover the influence of real supervisory methods, educators’ approach and happiness on skilled improvement.