Purpose: Many countries receive international support to strengthen professional capacity. The effect of these professional development activities (PDAs), however, is often negligible. This article provides useful insights on how international aid organizations could improve their PDAs, by describing an intervention developed and applied in Cambodia. This intervention aimed at developing a training approach to be used within the local ministry and increasing facilitation skills of government trainers in order to improve capacity building outcomes. Design/approach: The intervention incorporates contemporary (adult) learning theory and appreciates local expertise to the full. This was established through an educational design research (EDR) approach. EDR is a research methodology that is applied to design and test innovative interventions in poorly understood contexts. Findings: The intervention was successful in developing a capacity building approach and improved learning facilitation skills of ministerial staff. More time for collaboration, and incorporation of socio-constructivist and adult learning principles helped acknowledging the expertise of local staff. This had a positive effect on professional learning outcomes and ownership. Practical implications: The focus of this article is on the most important design principles for aid organizations and consultants for improving effectiveness of professional development and capacity building projects, and how to acknowledge and incorporate local expertise effectively. Originality/value: Usually, research into the effectiveness of professional development activities is limited to budgetary and organizational issues, leaving the learning component unexplored. This research excavates an alternative capacity building approach linking local expertise with contemporary knowledge on professional development. In addition, it contributes to the knowledge base on the learning component of PDAs and capacity building in Cambodia, both of which are poorly described in academic literature. The outcomes are also valuable for other contexts in which professional development and adult learning are involved. (Contains 6 tables and 3 figures.)