The increasing recognition of non-cognitive skills has led many researchers to investigate how educational practices enhance these skills. In this paper, we focus on the non-cognitive skill known as 'grit', and we study the relation between class size and grit in early grades. Using data from follow-up surveys of Project STAR, we show that fourth-grade pupils who experienced small classes during early grades are 0.12 standard deviations higher in grit than their peers in regular classes. Sub-sample analysis reveals that particularly boys and non-white pupils increase their grit in smaller classes. We also show that grit matters, because half of the effect of smaller classes on test scores entirely operates through grit.