While early research on full-day kindergarten (FDK) extolled its benefits for children's outcomes, later research demonstrated that children in half-day kindergarten (HDK) outperformed academically in the long-term. This study examined the longitudinal changes in kindergarten demographics and child outcomes by comparing data from the Early Childhood Longitudinal Survey (ECLS-K) 1998 and 2011. Results showed significant changes to kindergarten in general and with regard to FDK and HDK schedules. Two trends are discussed. Firstly, a significant increase of families living in poverty may have led to the expansion of FDK as an early intervention model. Secondly, across both cohorts, children attending HDK outperformed children attending FDK on academic measures in third- and fifth-grade suggesting the presence of a burn-out effect.