This study explored primary school teachers' self-efficacy beliefs about interdisciplinary teaching practices related to science, technology, engineering, arts and mathematics (STEAM) education and project-based learning to understand teacher perceptions and practices and to recommend some teacher training according to the national curricular standards in Brazil. Qualitative data were gathered using semi-structured interviews carried out with in-service teachers, which were supplemented by a questionnaire featuring both closed-ended and open-ended questions. The data were subsequently subjected to quantitative analysis. The findings reveal that while most teachers are familiar with and incorporate project-based learning into their pedagogical approaches, their awareness of and training in STEAM education are limited. Nevertheless, teachers perceived themselves as being very competent across most STEAM domains, including interdisciplinary curricular integration and projects. Chemistry, physics and arts are exceptions, with lower levels of teacher self-efficacy when compared to the other disciplines. This article examines the implications of these findings for pedagogical practices and teacher training in Brazil, while addressing what are teachers' current perceptions of STEAM practices, encompassing project-based learning and interdisciplinarity. It identifies the training requirements necessary to enhance their confidence in teaching science, while integrating arts-related subjects.