The Particle Physics Masterclasses are events offered by the “Netzwerk Teilchenwelt”, a German network of particle physicists, students and teachers with the intention to make original data from CERN available for own measurements of students. These events were evaluated in 2011/12. The investigation deals with their effect on the interest development of the youth participants, especially in particle physics. With a focus on the role of different event properties, it can be shown that besides the perceived challenge and comprehension, also authenticity is an important factor for the students´ interest development.