This paper presents the major findings and recommendations from a formative evaluation of the first of a 2-year in-service training program. This program was designed for the professional development of math teachers. It was developed following an educational reform, which was meant to enhance the teachers' ability to generate changes in their teaching methods and implement them in class. The teachers' attitudes towards the program were examined using close-ended questionnaires and open-ended questions which were administered to 19 teachers at the end of their first year of inclusion in the program. The research findings attested to the contribution of the program to the teachers' development - mainly to those with longer experience in math teaching -- in the area of the taught discipline itself, as well as in the didactic-educational area and the personal-emotional area. These findings were anchored in a conceptual framework of a model of the development of the teachers' nature of concern and interest regarding the change. The article discusses the potential instrumental and conceptual application of the findings in a focused decision-making process pertaining to running the program, and to a research-based accompaniment of the implementation process of professional development programs.