Background: Existing writing self-efficacy instruments have focused on assessing writing self-efficacy through examining mechanical and process features of writing to the neglect of the situated context and its influence. Purpose: The purpose of this thesis was to theoretically construct the concept of writing self-efficacy from a cognitive and socially constructed perspective and then measure writing self-efficacy from within the discipline of nursing. The initial phase required exploring the epistemological compatibility of self-efficacy theory and social constructionism. The culmination of this work was a multiphase multimethod project to develop and test the Situated Academic Writing Self-Efficacy Scale (SAWSES) based on Bandura’s self-efficacy theory and a model of socially constructed writing. The thesis presents five individual papers by publication – two published and three submitted for publication. Methods: Four independent sample studies were conducted. Two studies formed the tool editing phase: a Delphi panel with 7 nursing and 8 writing scholars and Cognitive interviews with 20 undergraduate students. Study validation required two sample recruitments. Study 1 surveyed 255 nursing students examining exploratory factor analysis and a structural equation model. To enhance generalizability, Study 2 surveyed an interdisciplinary sample of undergraduate (N = 543) and graduate students (N = 264) to conduct a multi-group confirmatory factor analysis. Results: The three identified factors present a structure to the questionnaire which is developmental and has the potential to detect gaps in student self-assessed ability to master various facets of disciplinary writing: 1) Factor 1 – Writing Essentials (synthesis, emotional control, language); 2) Factor 2 – Relational-Reflective – assesses relationship building with writing facilitators (teachers, academic sources) and the self through reflection; and 3) Factor 3 – Writing Identity – explores gaps in student achievement of transformative writing (creativity, voice, and disciplinary identity), where confidence can help identify the most engaged writers. Structural equation model procedures identified that writing apprehension and supportive environment were the strongest predictors of SAWSES scores. Conclusions: Findings from these studies support reliability and validity for SAWSES. SAWSES will offer educators a validated tool to research student writing self-efficacy, stimulate student reflection on writing, and significantly inform writing pedagogy.