Despite a sustainable research interest in different forms of teachers' professional development, scant international attention has been paid to forms of professional development which are implemented in South America. Based on a qualitative research design, this study explores the impact of the ateneo as an innovative model of continuing professional development. An ateneo is a model which supports teacher reflection and change in teaching practices by concentrating on context-responsive practical issues such as lesson planning and delivery. The study was carried out with 22 teachers of English as a foreign language in southern Argentina. Data were gathered through the teachers' lesson plans, whole group discussions, and the teachers' final assignments to receive credits for completion of the ateneo. Drawing on thematic analysis, the participants envisaged the ateneo as a practice-oriented, dynamic, interaction-based, and personal as well as collective space for developing teaching skills and professional knowledge. In particular, findings show that the participants exhibited an improvement in lesson contextualization, sequencing and transitioning, maximization of resources, class time management, and reflective teaching. The study argues that the ateneo became successful given the shared teacher identity among the participants and the course tutors, and the explicit focus on the teachers' daily practices.