The paper will contribute to theoretical approaches of teacher professional development by widening the perspective to professional learning communities (PLC) as a central element in the theoretical framework of organizational learning (Senge 1990; Holtappels 2013). Professional teacher development cannot only be attributed to pre-service and in-service training. Development processes regarding the acquirement of beliefs, attitudes, knowledge and competencies of teachers take place as well during everyday practice and depend on the learning environment of teacher’s workplace inside school. Rosenholtz (1991) showed, that basic orientations on school level, shared goals, teacher evaluation, common decision-making and intensive collaboration provide a bright scope of opportunities for professional learning by interaction with other teachers. PLCs enable teachers for collaborative work as a crucial condition for organizational learning. Professional teacher collaboration in institutionalized teams on a high level of PLCs show characteristics of teamwork that consists in reflexive dialogue, continuous analyses, shared goals and values, intensive communication about teaching and learning, cooperation for enhancing the effectiveness of teaching with focus on student’s learning (Leithwood 2000; Hall & Hord 2001; Eaker et al. (2002). International research findings show: Institutionalized teams relieve goal orientated acting, intensive exchange, enhanced pedagogical competencies, shared decision making, planning and problem-solving (Rosenholtz 1991). Collaboration in teacher teams provides opportunities for individual learning and supportive environments for professional development of teachers on one hand, for organisational learning to build capacity of change for effective school improvement on the other hand (Leithwood 2000; Stoll 2009). Several studies show impacts of PLC-acting on teaching quality and students’ learning (Louis & Marks 1998; Vescio, Ross & Adams 2008; Sigurdardottir 2010). The own data are based on three studies on school effectiveness in German primary and secondary schools: a) autonomy of schools (n=70 schools), b) ADDITION study about impacts of school and classroom factors on student competencies (n=54 primary schools), c) development of all-day schools (n=67 primary schools). Results: Most of the teachers in teams report benefits from working in PLCs on all dimensions of PLC-aims: Teamwork as PLC provides a supportive environment, opportunities for further learning and improvement of teaching. Teacher in PLC-teams have gained an encouraged acting concerning goal orientation and focus on student’s learning but with low scores on enhancing effectiveness of teaching and on analysis, diagnosis and evaluation in their pedagogical practice. However teacher collaboration by acting with characteristics of PLCs contributes to quality of differentiated teaching practice and to teaching development efforts.

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