Resumen: Writing and defending a thesis is a requirement to earn a university degree. Previous findings indicate that self-efficacy is related to academic performance. However, no existing tools register students’ perception of efficacy towards writing and defining academic texts. Our purpose was to develop and validate such a scale. Scale scores content, structural, convergent, and criterion-related validity as well as the measurement invariance across sex was evaluated using data from 418 students from 23 Spanish universities. Our findings showed that the scale holds a unidimensional structure that is invariant across sex. Data also supported the convergent validity, with correlations with self-efficacy and anxiety measures. The scale could track the effect of an educational intervention designed to improve students’ writing and defending academic texts skills, and the scores were related to performance on a writing task. Norms are provided to facilitate the interpretation of the scale scores. Idioma: Inglés DOI: 10.5093/psed2022a15 Año: 2023 Publicado en: Psicología educativa (Madrid) 29, 1 (2023), 91-99 ISSN: 1135-755X Factor impacto JCR: 1.7 (2023) Categ. JCR: EDUCATION & EDUCATIONAL RESEARCH rank: 257 / 756 = 0.34 (2023) - Q2 - T2 Categ. JCR: PSYCHOLOGY, MULTIDISCIPLINARY rank: 101 / 218 = 0.463 (2023) - Q2 - T2 Categ. JCR: PSYCHOLOGY, EDUCATIONAL rank: 46 / 74 = 0.622 (2023) - Q3 - T2 Factor impacto CITESCORE: 3.5 - Social Psychology (Q2) - Developmental and Educational Psychology (Q2)