Widening achievement gaps driven by socioeconomic disparity have become a global concern. Yet, few studies have been able to track the changes and developments of socioeconomic-achievement gaps (SES-achievement gaps henceforward) across time. Using PISA data from 2003 to 2018, we estimated family SES-achievement gaps in seven Asian education systems. The findings suggest that in mainland China the gaps are most pronounced, whereas in Macao, they remain consistently modest. Other systems fall in between these two extremes. Based on the new synchronic and diachronic pieces of evidence, we extrapolate possible explanations of varying SES-achievement gaps across education systems. We found that the gaps tend to be smaller when the low-socioeconomic students perform better in academic environments. Based on our analysis, we argue that if the policy goal is to reduce the learning gap associated with social and economic division, public attention in education should be directed towards students from disadvantaged backgrounds.