The study explored the correlation between students’ performance in national examinations in secondary schools and schools’ assessment policies in Trans-Nzoia County. The study involved 143 students, 39 teachers and 13 Directors of Studies in the selected secondary schools. The study used qualitative descriptive survey research design to collect and analyze the data. Data was collected through questionnaires, interview schedule guide and focused group discussion guides. The information from the questionnaires was presented in figures and percentages in tables while the information obtained from interviews and focused group discussions was analyzed using qualitative techniques. The findings of the study found a positive relationship between school assessment policies and students’ performance in national examinations. It was, therefore concluded that school assessment policies positively contribute to the academic performance of students in national examinations. The study thus recommended that regulations and policies should be put in place so that all schools can benefit from the practice and a uniform policy should be emphasized.