Teachers in primary schools often talk about children 'becoming readers' or 'being writers' but rarely do they speak of children 'becoming' or 'being' mathematicians. The discourse is more often around children needing to learn mathematics, a discourse that, significantly, maintains a view of the learner and mathematics as occupying separate spaces: the mathematics to be learnt is 'out there' and it is the job of the teacher to help the learner 'acquire' this mathematical content. In contrast, working with a mindset of learners as already being mathematicians (albeit inexperienced ones) has the potential to change the dynamics of classrooms as it acknowledges that learners are not empty vessels and that they have contributions to make to mathematics lessons. Teaching that builds on learners-as-mathematicians not only makes learning deeper and more engaging, leading to higher standards, but it also engenders in more children a desire to want to continue to learn maths. This book explores the theory and research evidence supporting this learners-as-mathematicians approach, and considers the practical implications.