Starting early in life, children, especially girls, experience obstacles when it comes to developing an interest in STEM. Although early childhood (EC) educators face an important task in promoting girls (and boys) in STEM, they often face challenges in doing so. Therefore, it is crucial for EC educators to cultivate positive attitudes, self-concepts, and STEM skills. To address these identified issues, a three-month professional development program was created for EC educators. This professional development program was evaluated using a pre–post design with a focus on the self-concept and gender stereotypes of EC educators. The program involved 30 female EC educators in evaluating these aspects. The statistical analyses show positive results in enhancing educators’ self-concepts and reducing gender stereotypes over the course of this professional development program. The results suggest the potential of the blended learning design in this professional development program and indicate that this program could serve as a promising model for future interventions.

Starting early in life, children, especially girls, experience obstacles when it comes to developing interest in STEM. Although teachers face an important task in promoting girls (and boys) in STEM, they often encounter hurdles in doing so. A three-month-long training for pre- and in-service teachers in elementary education was developed to counter this phenomenon. An important training feature was teaching ideas for STEM classrooms. Teachers’ evaluation of the training and teaching ideas, changes in their self-concept, and elementary students’ assessment of the teaching ideas were investigated. Students rated the teaching ideas favorably, with no gender differences. Even though each idea incorporated relevant didactic features for gender-sensitive STEM instruction, the teachers rated certain ideas and contents more critically than others. Nevertheless, their assessments speak in favor of the training intervention, while also indicating gaps in teachers’ professional knowledge regarding gender-sensitive didactics. Implications for the design of STEM teacher education are outlined.