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 cohorts. Results demonstrated that there were significant changes in kindergarten in general and with regard to FDK and HDK schedules between 1998 and 2011. These included differences in both demographics and academic performance. Two notable trends are discussed. Firstly, a significant increase of families living in poverty from 1998 to 2011 may have led districts to expand the availability of FDK as an early intervention model. Secondly, across both the 1998 and 2011 cohorts, children attending HDK outperformed children attending FDK on academic measures of reading and math in third- and fifth-grade suggesting the presence of a “burn-out effect”. These results are discussed in relation to the increasing academic expectations for kindergarten. (author abstract)