After enrollment in primary education in Kenya rapidly increased, there was a need to investigate how to improve the quality of education in Kenya. Inequity in primary education causes inequity throughout life. The purpose of this study is to examine the most influential factors that improve the learning conditions in primary schools in Kenya. Two research questions were set up for achieving this : (1) Which factors have more influence on student achievement, school factors or family factors? (2) What kind of factors determine higher achieving schools? The Hierarchal Linear Model (HLM) was applied for the achievement analysis. The data used here came from SACMEQ ? , an international learning assessment. The first research question examined the effect of SES on the achievement. The family background factor significantly affected reading scores, though single predictors were insignificant in explaining effects on student achievement. The second research question looked at the factors causing between-school variation in Kenya. There was a positive relationship between the aggregated socioeconomic status and the aggregated student achievement. School policy and other learning process factors might be potential issues for further study. A combination effect is also another area that can be further explored. It might be helpful to control the combination effect for estimating the pure relationship between academic achievement and family and school factors.