This design case presents the conceptualization, design, and development of Early Science Matters (ESM), an online teacher professional development (oTPD) program for early childhood teachers. The program design consisted of five primary features that were expected to promote participant learning, including (1) visually oriented content, (2) meaningful assessments, (3) chunking modules to build upon previous content, (4) reflective activities, and (5) encouraging website interactions with supplementary materials. Through a process of collaborative design between two faculty subject-matter experts and two professional instructional designers and media producers, we developed an initial version of the ESM program. After development, a focus group was recruited to test the first version of ESM initially. Subsequent revisions were made to the design based on the focus group evaluation. The case closes with a reflection on emergent challenges that we faced during the design process and the rationale for decisions made to address challenges.