Release of the PISA 2018 results revealed that Macao is not only a high-performing, but also fast- improving economy in three core literacies (reading, mathematics and science) in the past decade. Based on the publicly released data, this study seeks to validate that Macao’s remarkable progress in one main part is due to the lowering of the prevalence of grade repetition in the past decade. Secondary analysis of the Macao-PISA data was conducted, analyzing the trend of the rates of student grade repetition against the backdrop of the percentage of Macao’s 15-year-olds studying at the various grade levels. The trend over the six cycles of Macao-PISA assessment since 2003 shows that there is an increasing percentage of 15-year-olds studying at grade levels appropriate to their biological age with same-age peers. Admittedly, when more of the sampled students are studying at the modal grades, more of them possess favorable psychological dispositions and self-regulatory learning mechanisms. Consequently, they are able to reach or even excel beyond baseline performance standards. Thus, grade level of an age-based sample provides one convincing explanation on why Macao was commended for its fast improvement and high level performance in PISA 2018 in the past decade.