The COVID-19 pandemic has deepened the effects of socioeconomic status (SES) and wellbeing (WB) on students' academic achievement, particularly in developing countries; thus, it becomes necessary to understand the nature of these concurrent relationships. This study aimed to explore the relationships between SES, WB and academic achievement, based on the data from the Programme for International Student Assessment (PISA) in 2018 within the Turkish context. In this cross-sectional study, we used hierarchical multiple linear regression analysis to explore how the independent variables predicted academic achievement in blocks based on data from 6,890 students attending 186 schools. The study revealed that the model, including the independent variables, predicted students' achievement in reading, mathematics and science; however, the prediction level of demographic factors and domains of WB were very low, while SES had the highest prediction level. The results offer insights into the predictors of academic achievement and educational inequalities in the context of a developing country.