Early science, technology, engineering, and math (STEM) education matters for young children’s learning and their academic trajectories (McClure et al., 2017), but teachers must be empowered and supported to effectively teach STEM subjects to all children, including dual language learners (DLLs). This study focused on a curriculum-agnostic professional learning model (Brenneman, Lange, & Nayfeld, 2019), which was co-developed with educators to positively impact attitudes, beliefs, confidence, knowledge, and ultimately, teaching practice for preschool teachers around teaching STEM and working with DLLs. Forty-seven lead preschool teachers were randomly assigned to treatment or control conditions. Treatment teachers participated in over two years of connected, reflective, multi-level experiences linked to their practice. Results showed positive effects on intervention teachers’ attitudes, beliefs, and confidence towards teaching science, math, and working with dual language learners compared to control teachers. Treatment teachers also exhibited significant increases in pedagogical and content knowledge related to teaching STEM and working with DLLs, but no significant impacts on knowledge of teaching math (numeracy). Implications and future directions are discussed.