This chapter discusses the affective domain of self-efficacy, also described as self-belief, self-esteem, self-worth, self-affirmation, self-integrity, positive self-image, and the feeling of competence in writing and developing as a writer. Theory, research, and educational practices associated with developing children’s self-efficacy in writing and its important role in developing confident and effective writers are explored. This includes discussing the typical behaviours witnessed in a rich variety of educational research and differences observed in the behaviour of pupil-writers with high and low levels of self-efficacy. Finally, the authors describe the relationship between developing apprentice writers’ self-efficacy and the 14 principles of effective writing teaching. They give examples of the kinds of instructional practice carried out by the most effective teachers of writing.