Literature has pointed out, for at least two decades, that the perceptions about one’s own competency influence the motivation to learn and the school achievement. However, in the case of the Education for Youngsters and Adults (EJA), the beliefs and emotions related to the students’ own self-perceptions as learners, especially as Mathematics learners, have not been given proper attention. In this article, we present a case study whose purpose was to investigate possible mobilizations of the Mathematics self-efficacy beliefs by an EJA student throughout the development of Mathematics tasks, which were created based on a theoretical framework. The research – from the development of the activities through the analysis – was based on Albert Bandura’s Social Cognitive Theory, in particular, on the concept of self-efficacy. For seven months, we collected data through questionnaires, semi-structured interviews, the researchers’ field journal, and video recordings of a few Mathematics class of a high school class at a public school, in Divinópolis, Minas Gerais, Brazil. The results showed strong evidence of mobilization of the self-efficacy beliefs on Vanda’s behalf. However, albeit there has been observed more persistence by the student when carrying out her activities, her more active and autonomous participation, as well as her self-confidence and emotional well-being, it was also verified that the student’s behaviour, feelings, and perceptions under evaluative situations evinced a slight change with regards to controlling negative emotions in those situations. In spite of being a single case, this work contributes to shed light on the Mathematics self-efficacy beliefs held by EJA students, as well as on the teacher’s role in the process
