This paper reports on the development and pilot evaluation of a Croatian school-based youth gambling prevention program “Who really wins?”. The program is aimed at minimizing risk and enhancing protective factors related to youth gambling. A short-term evaluation of the program was conducted with a sample of 190 first and second year high-school students (67.6% boys, aged 14–17 years; average age 15.61). An experimental design with two groups (Training vs. No Training) and two measurement sessions (pre-test and post-test sessions) was used to evaluate change in problem gambling awareness, cognitive distortions, knowledge of the nature of random events as well as in social skills. Results showed significant changes in the post-test sessions, which can be attributed to changes in the Training group. We observed a decrease in risk factors, namely better knowledge about gambling and less gambling related cognitive distortions. Immediate effects on protective factors such as problem solving skills, refusal skills, and general self-efficacy were not observed. Findings also show program effects to be the same for both boys and girls, students from different types of schools, for those with different learning aptitudes, as well as for those at different risk levels with regard to their gambling, which speaks in favour of the program’s universality. The program had no iatrogenic effects on behaviour change and shows promise as an effective tool for youth gambling prevention. Future research and a long-term evaluation are needed to determine whether the observed changes are also linked to behavioural change.