Representational competence is an important component of learning Organic Chemistry. However, students are seen to be incompetent in translating from one kind of molecular diagram to another. An instructional method informed by spatial cognition research was designed and administered individually. The instruction involved having students check their solutions by attempting to match concrete models to their solution. The instruction helped students in the experimental group to identify their mistakes, understand the usefulness of concrete models and lead to large improvements in performance for the experimental group.