Early arithmetic skills, and in particular the understanding of the part-whole relationship, are currently considered crucial for future arithmetic achievement. They are complex skills extending far beyond the mastery of counting procedures. In order to develop these arithmetic skills in kindergarten children, we developed a game-based approach using conventional card and board games adapted to the targeted mathematical objectives. The present study examines the effects on the arithmetic skills of this game-based approach. Individual pre- and post-tests were administered to 194 children (5-6 years old) from four countries (play-based group n = 104 and control group n = 90). Our findings show that the learning outcomes of the game-based group were significantly higher than those of the control group after the intervention. The game-based group showed improvements in arithmetic skills, and in particular those relating to the part-part-whole relation. The intervention also resulted in all pupils, regardless of their initial proficiency level and including those regarded as 'at risk', making more progress than those in the control group. These results demonstrate the possibility of developing complex mathematical learning effectively in preschool in a manner consistent with the needs and interests of young children.