Teachers attend many courses, seminars, and workshops at the national and international levels to ensure their professional development. This study aims to investigate the opinions and achievements of the teachers who participated in the tenth Turkish Teacher Program (TTP) held at CERN. An explanatory case study was preferred as the research model. The study group consists of 12 teachers who participated in the CERN TTP-10 event. A semi-structured interview form was created to collect data. The form created by the researchers was finalized by taking expert opinions, and the final form consists of four questions. Interviews lasted approximately 30 minutes with each teacher. The descriptive analysis method was used in the analysis of the obtained data. In the results obtained, it is seen that the teachers aim to achieve the widespread impact of the program through students, teachers, and society. While doing this, they state that they can try many ways such as seminars, presentations, experience sharing, experimentation, and student clubs. Teachers' opinions about the program were generally positive, and they stated that their self-confidence and motivation about the effects of the lessons they conduct at school increased. It is seen that teachers want to extend the program period regarding the effectiveness of the program, reduce the theoretical lessons, and make more applications. As a result, the CERN TTP-10 activity positively affected the participating teachers. Increasing the number of such international events and ensuring that more teachers reach them is among the research suggestions.