This thesis is formed of two papers. The first paper is concerned with the construction and design of the Spelling Self-Efficacy Measure (SSEM), based upon the constructs that children have about learning to spell and findings from a literature search. The second paper further develops the SSEM, carrying out a large test administration and validation, and then exploring relationships between perceived efficacy beliefs and spelling ability. The rationale to create a measure of spelling self-efficacy originally stemmed from conversations with teachers during my placement experiences as a trainee educational psychologist. It was often the case that children in schools were not making progress in literacy, despite ongoing and high quality intervention and support. I carried out a literature review and found that the majority of spelling support packages were focused on building children’s mastery of skills rather than any focus on the emotional aspects of learning. I had many conversations with teachers about ways in which they could support children’s beliefs in their capabilities to learn, and had positive reviews with lots of school staff about how this had helped them make interventions more personalised to the child. The two papers in this thesis outline the steps taken to develop and construct the Spelling Self-Efficacy Measure. There were originally five domains underpinning the Spelling Self-Efficacy Measure: Belief in Own Ability to Learn to Spell; Belief in Learner Characteristics; Belief in the Need for Help from Others; Belief in Phonological Awareness; and Belief in Technical Understanding of Spelling. These five areas were condensed through analysis in both Paper 1 and Paper 2 to propose a revised Spelling Self-Efficacy Measure underpinned by three domains: Phonological Awareness, Learner Independence and Optimism in Abilities; Learner Confidence and Resilience. The Spelling Self-Efficacy Measure has been found to be a reliable and valid scale to explore children’s perceived efficacy beliefs about learning to spell. Consistent with existing research, significant correlations have been found between a child’s spelling ability and their level of spelling self-efficacy, as measured by the SSEM.