Using data from the Early Childhood Longitudinal Study--Kindergarten Class of 1998-1999, researchers considered the developmental trajectories of children when examining differences in math and reading achievement between kindergarteners who attended full-day and part-day programs.

"Perhaps the most troubling finding of the present study is that the academic benefits of full-day kindergarten subside soon after children leave kindergarten," the authors say.  Advantages of attending a full-day program have faded out by 3rd grade.

"The fade-out appears to be attributed to differences in the children and families that attend part- and full-day kindergarten, as well as school characteristics associated with kindergarten program type," write the authors.

Some of the biggest differences between the two populations was in racial backgrounds. A greater proportion of children in part-day kindergarten were of Hispanic, non-Hispanic White, Asian and multiracial backgrounds. A greater percentage of children in part-day kindergarten (14%) vs. full-day kindergarten (9.8%) came from a non-English speaking household. There were three times as many black children among full-day kindergartens than part-day kindergartens (22% vs. 7%). While part-day kindergarteners were more advantaged socioeconomically than full-day kindergarteners, the full-day children had higher levels of academic achievement in the fall of kindergarten.

Poverty rate among part-day kindergarten students was 6% lower than for full-day kindergarten students. Among part-day kindergarten students, the highest level of parental education was slightly greater, the proportion of children from married parent households was higher and the percentage of children from households with parents who had never been married was lower.

More socioeconomically disadvantaged full-day kindergarten students may be attending schools of lower quality compared to those attended by part-day kindergarteners, the researchers say.

"A Developmental Perspective on Full-Versus Part-Day Kindergarten and Children's Academic Trajectories Through Fifth Grade" by Elizabeth Votruba-Drzal et. al, Child Development, July-August 2008, volume 79, Number 4, pp. 957

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