Despite the burgeoning enthusiasm for the implementation of International Baccalaureate (IB) education within the Korean public education system, there is a paucity of research investigating the effects of IB PYP on student learning outcomes. In order to reduce the research gap, we conducted a longitudinal study to track the progress of 212 third-grade students at IB PYP World Schools over a period of three years. Using a propensity score matching method with socioeconomic status and private tutoring experiences as covariates, we statistically sampled 212 third graders attending to non-IB PYP schools as a control group. The results from repeated-measure analyses of variance revealed that students attending IB PYP schools exhibited superior academic achievement and motivation in Korean language and mathematics, compared to students in non-IB PYP schools. The impact of the implementation of the IB PYP was more pronounced when students were third graders than when they were fifth graders.