The spread of globalization means an accompanying growth in the importance of English as a lingua franca. Efforts to increase English proficiency are especially pronounced in Southeast Asia with the opening of the ASEAN Economic Community in 2015. A common strategy to enhance English learning in Asian countries is to begin instruction at the primary level, but policymakers face the challenge of preparing teachers of young learners with the necessary content and pedagogical knowledge to provide high quality English education. This article reports on a professional development effort aimed to help Thai primary teachers of English integrate communicative language teaching approaches. After describing the Thai English education context and key project components, the author uses participant and trainer response data to identify factors that contribute to perceived quality of the project. From these findings, the author makes recommendations to re-conceptualize best practices in teacher professional development for Thai English teachers. Findings and recommendations are applicable both to Thailand and to other nations with EFL contexts.