Abstract: The study explored effects of school based factors on academic performance in public primary schools in Njiru Sub-County. Academic performance is a product of socio-economic status, psychological and environmental factors. Education in Kenya plays an important role in every part of life for instance political, economic and social development. Secondary school placement and admission depends entirely on the achievement in the Kenya Certificate of Primary Education (K.C.P.E) in standard eight. Today even sponsorship that children from poor parents are supposed to benefit is offered according to the performance in the K.C.P.E results.