This mixed methods designed-based research (DBR) study explored one iteration of an online teacher professional development (oTPD) course about K-8 English language pedagogy. The study examined 85 educators' beliefs pre- and post-course about teaching academic and literacy content to English Language Learners (ELLs) and analyzed their discursive engagement. Quantitative findings indicated that the course positively impacted participants' beliefs no matter their professional characteristics (i.e. educator type, grade levels taught, and years of experience in education). A thematic analysis of forum posts revealed competing patterns of "unsituated pedagogical discourse," in which participants wrote about course content in isolation, and "situated pedagogical discourse," wherein participants contextualized and extended course content within their unique professional contexts. The discussion describes study findings in relation to existing DBR and socio-constructivist theory and includes design recommendations to increase participant use of "situated pedagogical discourse." Implications for future research and oTPD course design are included.