This study explores the use of a corpus of classroom discourse data (Singapore Corpus of Research in Education or SCoRE) to facilitate the professional development of English language (EL) teachers in Singapore. A survey was first conducted to probe the knowledge base and belief system of EL teachers in three key domains: epistemology, pedagogy, and discourse. This was followed by a discourse analysis of the SCoRE corpus to mine resources that could address the specific professional needs of teachers identified through the survey. Survey findings suggest that EL teachers in Singapore are less secure in epistemology than pedagogy or discourse-related issues. The efficacy of using corpus-based materials to help teachers reflect on and develop their professional competencies was tested through a workshop. The paper concludes with a discussion of the implications of using authentic and situated corpus resources to facilitate teachers' reflective practice and professional development.