In 2010, Governor Arnold Schwarzenegger signed the Kindergarten Readiness Act into law. The law changed the kindergarten entry cutoff so that children must turn five by September 1 to enter kindergarten. The law also established a new grade level--Transitional Kindergarten (TK)--which is the first year of a two-year kindergarten experience for students who turn five between September 2 and December 2. It specified that the new grade level be taught by credentialed teachers using a modified kindergarten curriculum that is developmentally appropriate, with the goal of promoting their success in school. The rollout of the Act has given rise to questions about how TK is being implemented in districts throughout California. This second research brief in a series highlighting findings from the "Study of California's Transitional Kindergarten Program" focuses on characteristics of TK classrooms compared with those of kindergarten classrooms. Based on surveys of TK and kindergarten teachers included in this study, it appears that TK teachers are adopting instructional practices that are more developmentally appropriate for the younger students enrolled in the program, as intended by the law. Students in standalone TK classrooms tended to spend more instructional time on social-emotional skill development and less time on reading/ELA and math than students in standalone kindergarten classrooms. In addition, students in standalone TK classrooms spent more time in child-directed activities and less time in whole-group activities compared with students in standalone kindergarten classrooms. However, findings in this research brief also point to the challenge of providing differentiated instruction, especially in combination classrooms. [For "Study of California's Transitional Kindergarten Program: Report on the First Year of Implementation," see ED609102.]