The paper, based on a primary survey, explores the inequalities in access and household investment on the market-based 'supplemental educational services' (SESs) in post-compulsory school education (i.e. secondary level of education) in Haryana, a northern state in India. We find that around 44% of students access SESs in secondary education in Haryana, and it varies considerably across socioeconomic groups such as class, caste and gender. Results from the two-step Heckman selection model suggest that access to and household investment in SESs is significantly determined by household factors and school characteristics. We also find that SESs in Haryana are not homogenous, vary widely in content delivery and private costs. Nearly 56% of the students (mainly from socio-economically underprivileged groups) attend the low-cost and low-quality private tuition centres, while their better-off counterparts attend the more organised medium- and high-cost tuition services, and this widens the already existing inequality in educational opportunities in the state. The study suggests to stringently regulate the flourishing commercial SESs market to minimise growing educational inequality in the state.