Transitional kindergarten--the first year of a two-year kindergarten program for California children born between September 2 and December 2--is intended to better prepare young five-year-olds for Kindergarten and ensure a strong start to their educational career. The goal of this study was to measure the success of the program by determining the impact of transitional kindergarten on students' readiness for kindergarten in several areas. AIR researchers compared language, literacy, mathematics, executive functioning, and social-emotional skills at kindergarten entry for students who attended transitional kindergarten and for those who did not. This brief outlines the results of the study, "Impact of California's Transitional Kindergarten Program, 2013-14," and suggests next steps for further research. [For the full study "Impact of California's Transitional Kindergarten Program, 2013-14," see ED563818.]