Based on the Sociocultural Theory of Mind (Vygotsky 2004) this qualitative study explores the development of novice TAs’ cognition in relation to FL teaching and applies dynamic assessment procedures (Sternberg and Grigorenko 2002, Lantolf and Poehner 2004) to the concrete practices of teacher education and supervision. The following questions frame the study: 1) Do novice TAs apply pedagogical knowledge from coursework on FL teaching to their own classroom practices and, if so, how? and 2) How can teacher supervision and specifically the use of dynamic assessment assist in the development of principled practice based on pedagogical content knowledge and not mere experiential knowledge? Data collected during Spring 2007 and Fall 2007 will be presented to illustrate how DA principles and procedures can be utilized to foster development of pedagogical expertise in a university FL context.