Abstract: We quantify the influence of teacher assignment on student test scores atthe high-stakes grade twelve examination in state-run schools in Delhi, India. We find that being assigned to a one standard deviation better thanaverage teacher moves a student at the median of the achievementdistribution to the 72nd percentile. The impact size is much higher thandocumented in existing literature, revealing that teachers play a muchbigger role in the context we study. Consistent with earlier studies,standard observable characteristics such as educational qualifications areunable to predict an effective teacher. For the first time we examinewhether personality traits matter, and find that ‘Openness’, as opposed tobeing closed to experiences, positively correlates with a high qualityteacher and ‘Conscientiousness’, as opposed to being flexible, has anegative correlation.