This study investigated the extent to which primary and secondary school pupils believe in cultural interpretations of the biological concepts of conception, birth of twins and sex determination and the influence of education level and gender. Cross-sectional survey research design was used. The target population was Standard Seven (7th grade in the primary school cycle), Form one and Form Three (1st and 3rd grades in the secondary school cycle) pupils in 10 districts in Kenya. A total of 3452 pupils (1875 girls and 1577 boys) participated. The pupils were drawn from 15 primary and 31 secondary schools. A questionnaire was used to gather information from the pupils. The findings indicate that pupils believe in the cultural interpretations of biological phenomena investigated. The findings further indicate that there is a relationship between the pupils' believe in cultural interpretations and the academic grade level and gender. The findings from this study, therefore, inform curriculum developers that cultural believes are likely to militate against the pupils' learning of science. It is recommended that teachers discuss cultural interpretations of scientific concepts before introducing them in their lessons.