This study introduces Pedagogic Causal Mechanisms (PCMs) in vocational education as a way to analyse and improve teaching and learning. PCMs are specific processes that directly connect educational inputs to learning outcomes. This paper uses an automotive mechanics lesson in Eswatini to show how PCMs work, focusing on Variation Theory as an example that creates an 'Ah ha moment' for students. Variation Theory demonstrates PCMs by highlighting key features through simple contrasts while keeping other elements constant. The research first describes the lesson in detail, then uses broader theories of vocational pedagogy to analyse it. It then introduces causal mechanisms as a concept, before defining PCMs more specifically. After explaining PCMs, the study shows how they provide particularly useful educational explanations, enhance professional judgement, and work with other PCMs to build situation-specific causality plans.