In this study, it was aimed to determine whether the professional development activities or participation in in-service education/training of teachers has an effect on their students’ science achievement or not. If such an effect exists, an attempt has been made to state which teachers should primarily participate in, or be directed to, education or such activities. The study was the survey model and TIMSS 2015 data was used. The study was conducted with the participation of 112871 students who were participated in TIMSS 2015 8th grade and their 5214 science teachers from European countries. Teachers were clustered into three groups (low, moderate and high) according to their participation in in-service training activities. The results show that the participation of teachers in in-service training makes a significant positive contribution to the success of their students. In the in-service training, “level of formal education completed”, “major area of study”, “years spent teaching”, and “sex of teacher” are important. As the level of education increases, the teachers become aware of their deficiencies and are more inclined towards in-service training. European countries or the European Union firstly recommend in-service training for teachers with a “short-cycle tertiary and bachelor’s or equivalent” level of formal education, and teachers whose “major area of study” is in an “other area” and is not in “education-science” are directed.
In-service education, professional development activities, science teachers.