In public schools, particularly in Kimilili Sub-County, student transfers are commonplace; nevertheless, the results of current empirical research on the impact of these transfers on students' academic performance are inconclusive. This study assessed the effects of student transfers on academic performance in public primary schools in Kimilili Sub-County, Kenya, because academic performance in public schools in the sub-county has been below average and the influence of these transfers on academic performance are not known. The research accomplished two goals: determined the impact of psychological factors on students' academic performance and ascertained the influence of social factors on the academic performance of transferred students in public primary schools respectively. The study used a mixed methods approach with a target population of 470 head teachers, 150 class teachers, and 308 pupils who transferred to different public primary schools. Data was collected through questionnaires, focused group discussions, and key informant interviews. The study used SPSS for quantitative analysis and thematic analysis for qualitative analysis. The Cronbach Alpha coefficient method confirmed questionnaire reliability, and expert evaluation confirmed content and construct validity. The study found that social and psychological factors significantly impact students' academic performance. The Pearsons correlation coefficient method yielded (r=0.671, p=0.001< 0.05) for social factors and (r= 0.714, p=0.000 < 0.05) for psychological factors respectively. Qualitative data also confirmed the results. These findings are crucial for addressing challenges faced by students and contribute to existing literature on pupils’ transfers and academic performance especially in public primary schools. Based on these findings, schools, TSC, and Ministry of Education should develop guidelines for transferred pupils, strengthen guidance and counseling programs, and build teacher capacity. This study supports further research on the influence of pupils’ transfers on their academic performance in private primary schools