The study sought to find out influence of pupils' cognitive abilities to task performance. Pupils from public and private schools participated in the study. Cognitive tasks administered were; length, continuous substance, mass and volume. Study used survey design by oral interviewing of pupils. Probability sampling technique was used to select 333 pupils from eight public and private primary schools. Sample of 164 pupils was randomly selected, with 50.6 % boys and 49.4% girls. Pupils from private primary schools performed better than those from public primary schools. Boys performed better performance than girls in all cognitive tasks given. Study established that school environment made difference in cognitive task performance of pupils, and this was attributed to improved learning and provision of basic learners' needs. Study recommended stakeholders in education of children come on board to provide facilities and materials necessary for creation of conducive learning environment in public primary schools in Kenya.