Science teachers explain concepts to students to improve their understanding of scientific phenomena, however, in order to be effective, a science teaching explanation needs to be adapted to the prior knowledge, ability, and motivations of specific learners. The effectiveness of science teaching explanations can be evaluated by considering the following components: response to learners; tools for adaptation; structure; clarity; highlighting relevance; timing within learning sequence; and accuracy. A multiple case study methodology was used to explore the ways in which teachers adapt these components when explaining concepts to different classes. Three science teachers were observed explaining concepts in their junior secondary science classes and subsequently interviewed to ascertain reasons for why they chose to explain concepts in a particular way. Content analysis was used to identify key themes. Findings indicated that the teachers adapted their explanations in their classes by varying their (1) response to learners, (2) use of tools for adaptations, (3) learning sequence, depth, and pace. Teachers described student factors which influenced their explanations, including student (i) ability, (ii) attitude towards science, (iii) response during the lesson, (iv) behaviour, and (v) interest. These factors were identified as the dominant cause of differences in explanations between classes. Other influences included contextual factors including time availability, physical classroom and class size, and the different teachers’ views on pedagogy. These findings indicate that science teaching explanations can be responsive rather than transmissive, with implications of this study indicating that asynchronous video explanations should not be considered as direct replacements for classroom explanations. Professional development relating to science teaching explanations should include ways to adapt explanations to the prior knowledge, ability, motivations, and interests of particular students, to improve comprehension, engagement and accessibility.