Teaching Biology and Geology as Reflective Decision-Making: Designing an Asynchronous Online Professional Development Course for In-Service Science Teachers

Professional development in discipline-specific pedagogy remains a persistent challenge in teacher education, particularly when addressed in fully online, asynchronous settings with in-service practitioners. This article describes and theorises the design of Specific Didactics of Biology and Geology, a 14-week professional development course offered at Universidade Aberta, Portugal’s public open distance university, within the framework of the institution’s Pedagogical Model. The course targets in-service Biology and Geology teachers enrolled in the first year of a teacher professionalisation programme. Rather than reporting a completed impact evaluation, the article offers a theoretically grounded, design-oriented practitioner inquiry account of course design, early implementation reflections, and transferable design principles for asynchronous online teacher professional development. Its conceptual core is the framing of teaching as didactic decision-making, integrating reflective practice, didactic transposition, and experiential learning theory into a coherent design philosophy that places participants’ existing professional experience at the centre of learning.The article argues that subject-specific professional development can be meaningfully designed in a fully asynchronous online format, provided that the e-activity repertoire is epistemically varied, experientially anchored, and coherent with the pedagogical principles under study. Three structural features are discussed in detail: a two-tier activity design distinguishing non-assessed preparatory tasks from assessed e-activities; a deliberately diverse typology of digital activity formats, each serving a distinct cognitive and social function; and an integrative culminating task, the Professional Development and Pedagogical Action Plan, developed progressively across the final three weeks of the course.By describing the course design in sufficient detail to enable adaptation to comparable contexts, the article contributes to research-informed approaches to online teacher professional development. It highlights the pedagogical potential of asynchronous learning environments when they are designed not as simplified substitutes for face-to-face provision, but as coherent spaces for reflective, situated, and discipline-specific professional learning.