This is an intriguing article because of its black/white dichotomy. The superiority of full-day or half day kindergarten has not been fully established especially in light of the many different kinds of Kindergartens existing in the US today (Graue, 2006 in Gullo, 2006).
Reserach shows that although children in full day kindergartens out perform those in half day programs in terms of reading and mathematics, those advantages begin to fade right after they leave for first grade (Votruba-Drzal, La-Grining, & Maldonado-Carreno, 2008). In fact, by the time third grade rolls around, both types of children do about the same scholastically, socially, emotionally, and physically. Ready for some more confusing info? Children in half-day programs do better than full-day children when you look at the whole rainbow of performance from First Grade all the way to Fifth Grade when children submerge deeper into academics.
It's not so clear cut.