The pupils’ poor performance in science in South African secondary schools is well documented. Therefore, it is deemed necessary to conduct a study that would portray knowledge structures for teaching a science topic. This is an empirical qualitative interpretive multiple case study looking at four physical science teachers teaching Doppler Effect to Grade 12 pupils. The data was collected through classroom observations and teacher interviews. Data analysis was done using concept maps. The results show that teachers’ knowledge as portrayed during the teaching lack coherence and to some extent the correctness that is expected of teachers. The weaknesses are considered likely to compromise their pupils’ conceptual understanding of the topic.