This study investigated the impact of a CALL teacher education workshop guided by the TPACK-in-Action model (Tai, 2013). This model is framed within Technological Pedagogical Content Knowledge (TPACK, Mishra & Koehler, 2006) and advocates a learning-by-doing approach (Chapelle & Hegelheimer, 2004) to understand how English teachers develop CALL competency and adopt the competency in their teaching. Participants were 24 elementary English teachers in Taiwan. The study used a mixed methods design (Creswell & Plano Clark, 2007), collecting and analyzing qualitative and quantitative data concurrently but separately before they were triangulated. Findings show that the TPACK-in-Action workshops had a positive impact on the 24 teachers. In addition to the development of CALL competency, it was also observed that participants demonstrated CALL competency in their teaching, such as selecting online materials and appropriate technology for content teaching, using cloud computing for student interaction, and matching the affordances of technology to meet their instructional goals and pedagogy. In sum, the study provides empirical evidence and a new perspective in the investigation of CALL teacher education. The theoretical and pedagogical implications for CALL teacher education research and practice are discussed.