Reasoning and problem solving are priority areas in the primary mathematics classroom. Participants will gain an understanding of how to develop these skills over the five years of secondary school, looking at the journey in reasoning from giving explanations through to developing formal proof. Bar modelling is a powerful tool for representing problems. Building on from concrete representations, this pictorial tool opens up pupil understanding in many curriculum areas including number relationships, all aspects of proportional reasoning and algebra. Participants will explore how bar modelling can be used to make sense of and solve complex mathematical problems.