ABC News: 'Freakonomics': What Makes a Perfect Parent?: "Steven Levitt and Stephen J. Dubner, co-authors of the best-selling 'Freakonomics,' pored through a massive government database called the Early Childhood Longitudinal Study. Starting in the late 1990s, it followed 20,000 American children, collecting information on many aspects of their lives. Levitt and Dubner used the ECLS to see what helps young children do well on tests.

'Not only does it measure their scores,' said Dubner. 'It also conducts extensive interviews with the families of the kids, so we know a lot about each family and what they do in the family.'"