This article examines two major aspects of effective school organizations in order to meet the challenges of the knowledge society. Firstly, it analyzes the role of schools as learning communities where a collective responsibility for quality teaching is being developed. Secondly, it presents the basic principles of teachers’ professional learning in the context of lifelong and life wide learning. Schools become vibrant communities (new social spaces) in which the teacher takes on new roles in a collaborative manner, and acquires new professional knowledge through action research and reflection. The ultimate goal of teachers’ professional learning is to improve students’ outcomes through comprehensive planning activities, instructional implementation and reflection. In this direction, a model of in-service training is proposed. It comprises of an epistemological framework of learning (Learning by Design) as well as digital tools of instructional design, collaboration and sharing. This approach can be applied at local, regional and national levels in order to serve continuing and basic education of teachers in Greece.