In 2010, Governor Arnold Schwarzenegger signed the Kindergarten Readiness Act into law, which changed the kindergarten entry age so that children must turn 5 by September instead of December to enroll. The new grade level was put into place to promote school readiness for California's youngest learners. It also established a new grade level--transitional kindergarten (TK)--which is the first year of a two-year kindergarten experience for students born between September 2 and December 2. When fully implemented, TK is intended to provide an additional year of early education to this group of children, with the goal of promoting their school readiness. With the support of the Heising-Simons Foundation and the David and Lucile Packard Foundation, American Institutes for Research (AIR) conducted an investigation of the planning and implementation of TK in the 2012-13 school year. This report--the second in a series highlighting findings from the study--builds on preliminary research activities to provide a more complete assessment of the status of TK in the first year of implementation. Findings include: (1) Some districts served transitional and regular kindergarten students in combination classrooms; (2) There was substantial variability in how districts approached implementation of the new grade level, including variation in the curricula teachers used to guide classroom instruction; (3) The most common challenges reported by districts implementing transitional kindergarten were funding, developing a transitional kindergarten report card, selecting curricula for the new grade level, and providing professional development for teachers; and (4) Parents participating in focus groups were pleased with the program overall and said they felt their children were benefiting from the additional support prior to kindergarten. [For the executive summary, "California's Transitional Kindergarten Program: Report on the First Year of Implementation. Executive Summary," see ED609103.]