Constructivism posits that the teacher's role is to help their students to actively construct new understanding for themselves. Diagnosis of students' prior understanding followed by carefully planned teaching sequences enables learners to grasp hitherto unknown concepts. Assessing whether they can then apply their new knowledge in new contexts verifies whether or not they have learnt what the teacher has taught. Using these three steps (diagnose, engage, evaluate) to structure a self-study highlighted the gap between rhetoric and reality in a science education methods course. This self-study research--which draws on journal entries; students' and colleagues' perspectives generated through questionnaires and interviews; and critical friends critique and questioning--had a significant impact on my teacher education pedagogy.