Teachers professional knowledge has been studied and theorized by different authors and perspectives: trying to identify it's components (Shulman, 1986), focusing on it's practical nature (Schön, 1983; Elbaz, 1983; Clandinin, & Connely, 1996) or situating it's different components in a reflexive (knowledge producer) practice (Alarcão, 2001; Sá-Chaves, 1994). In attempting to discuss it's specificity and professional nature, different contributions will be summed: from Sociology of Professions, from Education and Curriculum Theory and from History of Education. In a time when it's urgent, for the (de)professionalization of teachers, to address the question of how specific is the knowledge required to teach, we'll present five features of that specificity: 1. the composite and integrative nature mobilized to a situational use, 2. the analytical capacity, associated with reflective capacity in relation to the action taken, 3. mobilising and questioning nature, 4. meta-analysis, demanding distancing and self-critic, and 5. communicability and circulation. Examples of how that “specificity generator” elements of teachers’ professional knowledge were dealt with in initial early childhood teacher education research reports will also be presented for clarification.