California’s Kindergarten Readiness Act of 2010 established transitional kindergarten (TK), the first year of a two-year kindergarten program for students affected by the change in the birthdate cutoff for entry into kindergarten from December 2 to September 1.

This final report from the program’s evaluation focuses on results from a five-year study. The study used a rigorous regression discontinuity design to examine whether TK, as a new approach to prekindergarten education for age-eligible students, leads to positive outcomes, for which students, and under what conditions. The findings are based on direct assessments of over 6,000 kindergarteners in California in the fall and spring of the 2014-15 and 2015-16 school years, surveys of their teachers, and statewide data on students’ English language proficiency.

Key Findings

• TK gives students an advantage at kindergarten entry on a range of literacy and mathematics skills, including letter and word identification, phonological awareness, expressive vocabulary, problem solving, and knowledge of mathematical symbols and concepts.  Students who attended TK were also rated as more engaged by their teachers, compared to their peers. These advantages are notable given the large percentage (over 80%) of students in the comparison group who attended preschool while eligible students were enrolled in TK.
• TK is effective for all groups of students who participated. It showed a particularly notable impact on language skills for English learners and mathematics skills for low-income students at kindergarten entry.
• TK has no detectable impact on students’ executive function or incidence of problem behaviors at kindergarten entry.
• Impacts of TK are smaller at the end of kindergarten, though TK students continue to have an advantage over non-TK students on letter and word identification skills. Overall, non-TK students appeared to catch up with their TK peers on most measures, although both TK and comparison students demonstrated growth at or above what would be expected for their age on several assessments. The impact of TK on the literacy and mathematics skills of low-income and Hispanic students also persisted through kindergarten.
• There was little variation in the impact of TK by classroom or instructional characteristics. Standalone classrooms were not significantly different from TK/kindergarten combination classrooms in their impact; half-day and full-day classrooms showed similar effects; and differences in assessed quality of teacher-child interactions did not change the program’s impact. These findings suggest TK’s positive impact for students may be driven by the characteristics that TK programs have in common (and that make TK a unique approach to prekindergarten): credentialed teachers with bachelor’s degrees, close alignment with kindergarten, and inclusion of students from all income-levels.