A group of mothers and infants celebrate a recent graduation from the Harlem Children's Zone Baby College program. Marty Lipp/Courtesy of Harlem Children's Zone hide caption

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Julie Byard, head of a Detroit nursery, tells children stories and sings them songs prior to their afternoon nap in 1942. AP hide caption

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Francis Csedrik remembers details of being bonked hard on the head when he was 4, and having to go to the emergency room. Meg Vogel/NPR hide caption

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Teacher Denise Severing leads a math lesson at a Head Start school in Woodbourne, New York. John Moore/Getty Images hide caption

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