This study analyzes the potential link between medium of instruction and student performance at primary school level. Value added models pertaining to the effect of medium of instruction on student achievement are estimated using Young Lives longitudinal data of primary school children in Indian state of Andhra Pradesh and Telangana. Using Math scores to proxy for student achievement we find that Telugu (mother tongue) medium students on an average perform significantly better as compared to English medium students after controlling for students ability, household characteristics and parental aspiration. This analysis suggests that introducing English medium of instruction at earlier grades during school life may negatively affect learning outcomes of students.