To meet the increasing demand for change in the incorporation of ICT in education the Greek Ministry of Education and the Institute of Educational Policy of Greece, launched a nationwide project of in-service training (INSET) of teachers of the second level, training of teachers in the use and evaluation of ICT pedagogy in classroom instruction. The main focus of the study was to evaluate the implementation and effectiveness of this in-service training in the pedagogic use of ICT in classroom-based instruction. Through the data collected and analyzed it is argued that a successful training course could be associated with the selection and utilization of specific research and instruction theories. These theories tailored to the acknowledged different profiles of the teacher-trainees as well as the time and setting of the course could promote effectiveness and produce fruitful outcomes.