The aim of the study was to investigate the quality of diagrams and explanations of moon phases in grade 6 to 8 Natural Science textbooks; to establish whether the textbooks provide scientifically correct content information for learners and teachers and to investigate whether the textbooks used for teaching are effective conceptual development tools for grade 8 learners, specifically when exploring moon phases. The research consisted of two phases, where the first phase investigated the quality of textbooks, and the second phase investigating learners’ ideas about moon phases.