Background: The poor performance of learners in mathematics has long been a matter of concern in South Africa. The Annual National Assessment (ANA) results reveal that the problem starts in the foundation phase with number concepts. Aim: This research sought to ascertain how foundation phase teachers used mathematical resources to teach number concepts as this may be one of the contributors to poor mathematics results. Setting: The purposively selected participants included five foundation phase teachers teaching Grades 1-3 at two schools in the Western Cape, in South Africa. Methods: The research was located within the interpretive qualitative research paradigm and used a case study approach. Data were collected through lesson observations and interviews and analysed through the lens of Vygotsky's sociocultural theory. Results: The findings of this study revealed that teaching for understanding was often compromised by teaching to enable learners to pass systemic assessments. Teachers are inclined to rote teaching with drill work in preparation for assessments such as the ANA and the systemic assessment. Consequently, manipulatives are not necessarily used optimally or opportunely. Conclusion: This study recommends that teachers should receive the necessary training to use and follow Vygotsky's Zone of Proximal Development and also make an effort to follow the guidelines indicated in the Curriculum and Assessment Policy Statement mathematics document in respect of how and when to use practical mathematical manipulatives.