Sixty two elementary school teachers from 16 urban schools, participated in this study. These teachers participated in an Israeli government sponsored professional development program for three years. The purpose of the development program was to enhance teachers’ mathematical knowledge and pedagogical methods with regard to NCTM standards in mathematics. Teachers were exposed to the Israeli Ministry of Education mathematical curricular: numbers and operations, data, algebra, proportion, space, and shapes. Teachers’ knowledge was assessed each year in all professional development centres by uniform government tests based on the topics which were studied. In the beginning of the study there were no significant differences between the two groups in the following variables: Years of experience in teaching mathematics mathematical knowledge and PCK were assessed by government measures.