Greece and Portugal are two Southern European countries, with nearly the same population as well as a centralized educational system that follows the same vertical structure. Both countries were deeply affected by the economic crisis during the last decade. Despite being severely hit by the economic crisis, Portugal has advanced to the OECD average level in students’ mathematical performance in the Programme for International Student Assessment (PISA 2018), while Greece has performed below the OECD average. PISA, as one of the most influential international educational surveys, aims to evaluate educational systems and provides a valuable platform for comparisons. Portuguese students outperformed their Greek counterparts by 7 points in the first PISA 2000 and went on to widen the difference by 41 points in PISA 2018. In addition to having increased the average performance in Mathematics, Portugal has managed to reduce the percentage of low-achieving students and at the same time increase the percentage of high-achieving students. According to PISA 2018 reports, Portugal is the only member of OECD that has experienced significant improvement in mathematics performance of their students through its participation in PISA. In contrast, the performance of Greek 15-year-old students in mathematics has not improved and has remained below the OECD average since it participated in PISA. What national strategies have been set up and implemented in Portugal so as to foster student’s mathematical literacy competencies? A clear curriculum, students’ regular assessment, teachers’ training and the Action Plan for Mathematics. But despite that fact, the Mathematics performance of Greek 15-year-olds students in PISA in all cycles of PISA remains below the respective OECD average, in contrast with Portugal, that has registered a quantum leap (Crato, 2020). The main aim of this research is, through a recording of the Greek and Portuguese students’ mathematics achievements in PISA and at the same time of the Mathematics Education in both countries, through available policy documents and research reports, to comment on the current outcomes of the two educational systems and their students’ performance in Mathematics.