This paper evaluates the impact of an online game-based financial education tool on students' financial literacy levels. By conducting a Randomized Controlled Trial (RCT) involving 2,220 students across four countries in a multi-country experimental setting, we demonstrate that the intervention significantly enhances students' financial literacy levels by 0.313 SD. This study contributes to the emerging academic literature concerning the evaluation of financial education interventions that incorporate learning-by-playing. The participation of students from four countries adds relevance by facilitating cross-comparison of outcomes and stimulating discussions about country-specific factors and peculiarities influencing youth financial literacy.