We present results from the first study to examine the causal impact of early-childhood education on the social preferences of children. We compare children who, at 3–4 years old, were randomized into either a full-time preschool, a parenting program, or a control group. We returned to the children when they reached 6–8 years of age and conducted a series of incentivized experiments to elicit their social preferences. We find that early-childhood education has a strong causal impact on social preferences. Our findings highlight the importance of taking a broad perspective when designing and evaluating early-childhood educational programs. (author abstract)