The more parents talk to their children, the faster those children's vocabularies grow and the better their intelligence develops. This observation has profound implications for policies about babies and their parents. It suggests that sending children to pre-school at the age of four — a favored step among policymakers — comes too late to compensate for educational shortcomings at home. Happily, understanding of how children’s vocabularies develop is growing, as several presentations at this year’s meeting of the American Association for the Advancement of Science showed. One of the most striking revelations came from Anne Fernald of Stanford University, who has found that the disparity appears well before a child is three.