Foundation phase teachers in South African schools follow a socio-constructivist approach to the teaching and learning of mathematics, which entails that learners experiment freely with concepts and are encouraged to communicate and share their thoughts and ideas. In an effort to understand the impact that the physical learning environment, such as noise or large class sizes, have on learning in South African foundation phase classrooms, this study deployed a qualitative case study design to gain insight into the learning and teaching that take place in Grade 1 classrooms. From a cognitive load perspective, the study found that noise, as result of the large number of learners in the class, as well as noise from the outdoor environment, contributes to the overload of learners' working memory, which ultimately impacts negatively on learning. The study also found that the large classroom sizes in Grade 1 prevented teachers from rendering effective support, which causes uncertainty among learners in regard to what is expected of them when working on classroom tasks. This uncertainty leads to extraneous cognitive load.