High quality STEM professional learning is necessary for supporting early educators to implement early childhood STEM education in ways that promote young children’s development. This is particularly important for educators serving young children of color or from under-resourced backgrounds who have few STEM early learning opportunities. The STEM Lab intervention was designed to address multiple barriers early educators face regarding STEM education by providing designated time, space, materials and professional learning for teachers targeting STEM education. This study engaged 47 preschool educators serving primarily African American and Latinx children from under-resourced families in the STEM Lab intervention. Observational data identified higher quality teacher-child interactions in the STEM Lab lessons compared to regular classroom experiences, particularly for instructional quality. While STEM opportunities were rare in the regular classroom, multiple observations across the school year in the STEM Labs found that teachers used a range of quality science and engineering practices in the STEM Lab and improved in their skills across the school year. (author abstract)