The study sought to investigate the extent to which selected, school based factors contributed to pupils" low progression in primary schools in Trans-Nzoia West Sub-County. The study adopted ex-post facto research design. The target population was 1815 teachers drawn from 91 public primary schools. Data was collected from a sample of 313 teachers through self-administered questionnaires. Proportionate, stratified and simple random sampling techniques were used to select the subjects. The teachers" questionnaires were piloted in 5 schools in Bungoma North Sub-County and their reliabilities established after testing using the internal consistency method and Cronbach Alpha coefficient of 0.92 was realised. Data was analysed using both descriptive and inferential statistics with the aid of the Statistical Package for Social Sciences (SPSS) version 21. Data was described and summarised using frequencies and percentages while hypotheses were tested at the .05 level of significance and using simple regression analysis. The results revealed that school factors influence progression of pupils in the public primary school. The results of the study may inform the Ministry of Education, Boards of Management, parents and teachers in Trans-Nzoia West Sub-County and the country at large on factors to be addressed to enhance pupils` progression in public primary schools in the sub-county.