Educational equity has evolved into two distinctly different dimensions: fairness and adequacy. However, there is a lack of empirical studies exploring the relationship between educational fairness and adequacy. This study aimed to examine whether these two dimensions of equity tend to reinforce each other in practice or pull in different directions. Data for the study were taken from the most recent four waves of Programme for International Student Assessment. Focusing on the students’ math achievement, this study calculated educational fairness (the relationship between students’ socioeconomic status and their academic achievement) and educational adequacy (the percentage of students above the minimum standard; a Gini-type coefficient of academic achievement inequality). Based on the created variables, 28 OECD country panel data for the period 2006 to 2015 were constructed, and a fixed-effect model was used. The main findings of this study demonstrate that within-country changes in educational fairness are intertwined with adequacy. More specifically, the relationship between the SES coefficient and a Gini-type coefficient is positive, whereas no significant relationship is found between the SES coefficient and the percentage of students above the minimum standard. A negative relation is found between a Gini-type coefficient and the percentage of students above the minimum standard.