This paper examines the determinants of spending and the amount of time attending private supplementary tutoring, or commonly known as private tuition, in Malaysia. Based on 343 self-reported questionnaires with upper secondary students across three states in Malaysia and using multiple regression analysis, we identified ethnicity, father's level of education and past academic performance as significant determinants of spending and amount of time attending private tuition. However, interestingly, we found that while geographical location and participation in internal tuition in schools were also determinants of spending, these two were not significant in determining the amount of time attending private supplementary tutoring. The identification of determinants of spending and amount of time, and in addition, the differences between these two illustrates the economic and educational dimensions of shadow education. More importantly, the insight also contributes to the formulation of possible interventions that can improve quality and reduce inequality in the mainstream education system.