After disconfirming several potential explanations, such as better nutrition or differential parental treatment, researchers concluded that firstborn children’s higher IQs stem from a simple fact of family life: older siblings engage in teaching younger ones. Outside the family, laboratory research and real-world programs consistently show that engaging students in tutoring their peers has benefits for all involved, and especially for the ones doing the teaching. Why would the act of teaching produce learning—for the teacher? The answer is that teaching is a deeply social act, one that
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