Nowadays, low-fee private (LFP) primary schools are proliferating in the slums of urban areas in developing countries. It is believed that these schools can help to achieve Education for All by 2015. Although previous research has compared schools in slums with those situated beyond their borders, or gauged the relative merits of public and private schools in relation to school choice, few studies have made direct comparisons between schools situated within the same slum. The present study assessed the aspects of slum schools that contribute to school choice. It examined this by comparing 13 LFP schools in Kibera, the biggest slum in Kenya, to identify why some schools have more pupils than others. The survey findings show that schools with lower fees, demonstrably higher performance in the primary leaving examination, and free lunches attract more pupils than those that can only boast one or two of these attributes. The study also found that whether or not the school was officially registered with the Ministry of Education was not as important as the aforementioned factors. The study concludes that there are variations among slum schools and that slum dwellers invariably choose the school that is perceived to perform well. However, further study is necessary to identify why some schools with high fees and low performance still attract some slum children.