Kirstin Erath examines the epistemic role of explanations in classroom discussions, which are an important component of everyday mathematics instruction. She connects discourse analytical, interactionist, and epistemological perspectives in mathematics education to make oral explanations in mathematics teaching tangible as both a linguistic and subject-specific object. The author empirically reconstructs that 'good' explanations in the classroom are very differently structured. Furthermore, she shows that while explaining is an important medium for learning, it rarely becomes the subject of learning, which prevents learners with limited prior experiences from taking advantage of important subject-specific learning opportunities.