The aim of this research was to x-ray some causes of poor performance of pupils in primary school mathematics. Specifically, the study examined the use of instructional materials and pupils’ academic performance in mathematics; parents’ socio-economic background and pupils’ academic performance in mathematics; compared the performance of private and public primary school pupils in mathematics; examined ways in which teachers contribute to pupils’ poor performance in mathematics. The study employed a correlational and quasi- experimental research designs. A simple random sampling (...) technique was used to select a sample of 270 pupils and 45 teachers drawn from nine primary schools in Akamkpa local government area of Cross River State. A questionnaire and a mathematics achievement test (MAT) were instruments used for data collection. The collected data was analysed using a simple percentage (%) and arithmetic mean (X). The findings of the study revealed that the use of instructional materials adequately led to pupils’ poor performance in mathematics; parents’ socio-economic status contributed to the pupils’ performance in mathematics; pupils in private primary school perform better than their colleagues in public schools in mathematics; and teachers contribute to the poor performance of pupils in mathematics. Based on this results, conclusions and recommendations were made. (shrink)