This study investigated the effect of a STEAM (science, technology, engineering, arts, and mathematics) methods course on elementary preservice teachers' (PTs') perceptions of self-efficacy to teach engineering practices. The course positioned engineering as the primary content area from which to integrate other subjects. To enhance PTs' perception of engineering self-efficacy, the course provided instruction that leveraged the following sources of self-efficacy: cognitive content mastery, cognitive pedagogical mastery, vicarious experience, verbal persuasion, and emotional state. The study also examined to what extent the various sources of self-efficacy contributed to changes in self-efficacy. Data was collected from 14 participants that included a self-efficacy survey and focus group interview. After completing the course, elementary PTs' self-efficacy to teach engineering practices increased significantly. Qualitative data analysis revealed cognitive pedagogical mastery, vicarious experience (specifically simulated modeling), and emotional state were the most influential sources linked to positive changes in self-efficacy, with cognitive content mastery, and other forms of vicarious experience contributing, but to a lesser degree. These results suggest that teacher preparation programs can better support elementary PTs to teach engineering practices by offering additional methods courses focused on engineering, rather than providing short-term exposure to engineering practices and pedagogy in overloaded science methods courses.