This study contributes to teacher educators' pedagogical content knowledge by drawing on phenomenography-variation theory to (i) research and describe qualitative differences in Beginner Teachers' conceptions of pupils' understandings of subject content and, (ii) provide evidence of the effectiveness of an instructional strategy that might be adopted by teacher educators based upon those conceptions (known as 'Learning Study'). The study identified nine possible conceptions of pupils' understanding of the topic of 'price' in economics/business education with each being divided into a structural and a contextual element. These provide a useful framework for teacher educators to conceptualise Beginner Teachers' learning about pupils' understanding. In addition, Learning Study is shown to have a statistically significant, medium/large effect on the development of Beginner Teachers' knowledge of pupils' understandings in comparison to a control group. These results add to the evidence for adopting this approach more widely in teacher education.