There is a need for qualitative research into teachers' self-efficacy beliefs so that the relationship between these beliefs and other cognitions possessed by teachers, including their practical knowledge, can be better understood by teacher educators. Teachers' self-efficacy beliefs may need supporting if they seem too low or challenging if they seem too high. However, clear criteria are needed to facilitate assessment, together with the use of rigorous qualitative methods. This article explores these issues while reporting on research conducted in Oman into the cognitions of two in-service English language teachers. There is a focus on how qualitative case study research methodology was used to assess the degree of fit between teachers' reported self-efficacy beliefs and their practical knowledge, aiding subsequent intervention to support professional development. Implications for teacher educators and researchers are discussed.