<p style="text-align: justify;">The problems in education in the countries of the Organization for Economic Cooperation and Development (OECD) vary from country to country. The differences between "upper class" and "lower class" countries in PISA assessment results have led to a research gap. The purpose of this study was to (a) test students' mathematical literacy skills on the Program for International Student Assessment (PISA) test and compare the results using the sum of means across OECD countries; (b) examine the relationship between students' mathematical competence, precision, and self-perception of mathematical literacy skills in the PISA test; and (c) analyze the gaps that exist between the implementation of mathematics instruction in school and the mathematical literacy as measured on the PISA test. This study was designed as a mixed method with an explanatory sequential design. The data collection methods included test procedures, questionnaires, and interviews. The result of this study showed that the overall mean score obtained was below the OECD average. In general, the respondents achieved only level 2 mathematics proficiency. A significant relationship was found between mathematical competence, precision, and self-perception in mathematical skills. On the other hand, there was a gap, namely the difference at the implementation level, where mathematical literacy measured by PISA differed from the measurement of mathematical learning achievement by teachers in school. The results showed that teaching that emphasizes only problem-solving procedures affects low mathematical competence and is not useful enough for students to deal with the PISA mathematics test.</p>