When the Head Start Impact Study generally failed to show cognitive or behavioral improvements that lasted beyond kindergarten, Head Start’s defenders pointed to possible “sleeper effects” as a reason to keep the program going. The argument is that Head Start may have imparted a benefit that is not detectable in the elementary years but that emerges later on. A new paper from Brookings’ “Hamilton Project” follows in that tradition, claiming that Head Start improves high school graduation rates, college attendance, self-control, self-esteem, and parenting practices.