This article presents the STEMsmart early childhood teacher professional development model. The model is developed based on Clarke and Hollingsworth’s Interconnected Model and focuses on early childhood STEM education. The model includes components contributing to teachers’ change in four main domains: (1) Personal domain, (2) External domain, (3) Domain of practice, and (4) Domain of consequence. Initial trials of the model have significantly improved teachers’ knowledge and pedagogical practices related to STEM education. This model needs further research to gather convincing evidence confirming its suitability and effectiveness, providing a basis for scaling up and applying it to develop other professional competencies of early childhood teachers.