In this paper we report a large‐scale study designed to evaluate the impact of masters courses on the professional development of science school teachers and, consequently, on the improvement of the quality of science education. The underlying assumption of this study is that masters teachers are widely recognized as assuming a relevant role to establish bridges between education research and practices, not only as knowledge producers but also as mediators and privileged users of the knowledge produced by research. The empirical study was conducted with science teachers who experienced advanced professional education programmes, leading to masters degrees, in some specific areas of science or science education. Data were collected through a written questionnaire answered by 81 masters teachers who concluded their masters courses between 2001 and 2005 in 12 Portuguese universities. The results indicate that the majority of respondents (80%) considered the existence of an impact on their professional practice, namely, (i) stronger critical attitudes about the teaching and learning process, (ii) the use of more diversified (or new) teaching strategies, (iii) a deeper professional knowledge, and (iv) a higher confidence in discussions with their peers. Looking deeply at concrete examples of impact, the results show that 63% of answers were examples of micro‐impact, e.g. an impact in the classroom. However, some masters teachers (20%) mentioned little impact on their professional practice, as the content of the course was not articulated with the reality of school practices. There is an overlap of the results found here with other studies which suggests that there is still a need to increase the links between higher education universities, responsible for teacher education programmes, and secondary schools. The main obstacles to transferring research knowledge, developed during the masters course, to professional activities are found and some suggestions for overcoming them are proposed.