Ministry of National Education Turkey (MoNET) has undergone some substantial changes in primary and secondary school courses curricula. The former notion of the curricula has replaced with the constructivist learning theory based curricula starting from primary education courses to upward since the beginning of the millennium. This 'paradigm shift' required fundamental changes in terms of student and teacher roles, assessment methods and learning products. Some studies implied that besides some other skills, Turkish teachers should be supported in terms of nomenclature and teaching of Higher Order Thinking Skills (HOTS). Critical Thinking (CT) skill is one of the most important of the HOTS. In this study an in-service training was devised to support Biology teachers in terms of CT terminology, preparing activities that more properly emphasize on CT aspects, and objective assessment of CT skills. The in-service training course content will be shaped by the literature, teacher and expert feedbacks about the prepared content and the pilot application of the course. The main application of the course will be performed in the early 2011 on national or local level. (C) 2010 Published by Elsevier Ltd.