Magnuson, Ruhm, and Waldfogel conclude that early education does increase reading and mathematics skills at school entry.
However, the study also found that, in contrast to the general population in pre-kindergarten, disadvantaged children and those attending schools with "low levels of academic instruction" get the largest and most lasting academic gains from early education.
Currie and Thomas try to control for many family background factors. The analysis is based on within-family data, comparing children in Head Start with their siblings who were not in Head Start. Also, mothers who were themselves enrolled in Head Start were compared to their adult sisters who were not. Currie and Thomas analyzed groups separately by ethnicity: White, Black and Hispanic. White children, who were the most disadvantaged, showed larger and longer lasting improvements than African-American children.
Not all studies support the claim that Head Start is effective when measured by long-term gain. Many researchers acknowledge that Head Start appears to make a significant educational impact early-on but argue that these benefits quickly fade. This phenomenon known as “Head Start Fade” begins to show itself as early as second and third grade when students who attended Head Start programs begin to fall behind their non-participant peers. The concept of “ Head Start Fade” leaves government officials and educators left wondering what can be done beyond the preschool years to perpetuate the early gains made by enrollment in Head Start programs. For a more thorough exploration of this argument see: 1) Where Do Head Start Attendees End up? One Reason Why Preschool Effects Fade out Valerie E. Lee, Susanna Loeb Educational Evaluation and Policy Analysis, Vol. 17, No. 1 (Spring, 1995), pp. 62-82 doi:10.2307/1164270 2) Does Head Start Fade Out? S. Barnett (1993), Education Week, 5, 40 3) Long Term Effects of Early Childhood Programs on Cognitive and School Outcomes. S. Barnett (1995, Winter), The Future of Children, 5(3), 25-50