California students who had attended Transitional Kindergarten were more advanced than their peers in language, literacy, mathematics and executive function, early results of a study by AIR show. The differences amount to as much as a five-month head start in kindergarten. Transitional Kindergarten grew out of California’s Kindergarten Readiness Act, passed in 2010. Historically, the state required children to be 5 by Dec. 2 to enroll for kindergarten. When the new law moved the cut-off to Sept. 1, Transitional Kindergarten was created to serve those who turned 5 between Sept. 2 and Dec. 2.