The most concrete reason for doubting the wider applicability of the Perry Preschool and Abecedarian effects is this: A large-scale, high-quality replication of the Abecedarian approach failed to achieve much of anything. Called the Infant Health and Development Program, it was begun in 1985. Like Abecedarian, IHDP identified infants at risk of developmental problems because of low birth weight and supplied similarly intensive intervention. Unlike Abecedarian, IHDP had a large sample (377 in the treatment group, 608 in the control group) spread over several sites assessed by independent researchers. IHDP provided a level of early intervention that couldn’t possibly be replicated nationwide, but it gave us by far the most thorough test of intensive early intervention to date.

The follow-ups at ages 2 and 3 were positive, with large gains in cognitive functioning for the treatment group. But by age 5, those gains had attenuated. Where are things now? In the most recent report, the children in the study had reached 18. For the two-thirds of the sample who weighed no more than 2,000 grams (4.4 pounds) at birth, almost all of the outcome measures weren’t even in the right direction: The control group did slightly better. For those who weighed 2,001 to 2,500 grams at birth, the best news the analysts could find were positive differences on a math test and on a self-report of risky behaviors that reached statistical significance but were substantively small. Combine the results for both groups, and the IHDP showed no significant effects on any of the reported measures — not cognitive tests, measures of behavior problems and academic achievement, or arrest, incarceration and school- dropout rates.