Abstract--Previous studies focusing on teacher education have highlighted the role that supervised practicum plays in the construction of future teachers' personal beliefs, including self-efficacy beliefs, yet there remains a need to understand which learning experiences contribute to the constitution of this belief during the supervised practicum. Our objective was to identify situations that influenced student teachers' judgment of self-efficacy during the development of supervised practicum. This exploratory and descriptive documentary research analyzed 18 reflective portfolios produced by student teachers' during their supervised practicum in a physical education teaching program course. The experience of teaching in locus and the opportunity to experience everyday school-life were recurring situations in 15 out of the 18 analyzed portfolios. The results led us to believe that offering student teachers the possibility to meet and experience the teaching environment in advance contributed positively, through enactive mastery experiences, to the building of their self-efficacy beliefs concerned to teaching.