Ιn the present paper, a training effort organized by a school unit is being analyzed. A school unit of secondary education cooperated with some educational institutions and organized α professional meeting-workshop in order teachers to be familiarized with the collaborative approach of teaching. Initially, the article presents on the one hand principal’s role in the improvement of teachers’ skills and on the other hand, the reasons for teachers’
professional development. For the evaluation of this training effort, questionnaires were given to the participants. The analysis of the results showed that as far as their professional development is concerned, teachers wish the combination of theory and practice, their contribution to the topic and the cooperation of the school unit with all the educational institutions.