As part of its effort to make universal prekindergarten (UPK) available to four-year-olds, California has recently expanded transitional kindergarten (TK) in its public schools. TK will be a full pre-K grade level in all districts by the 2025-26 school year. Other states that seek to broaden access to early care and education (ECE) can learn lessons from the challenges California has faced as it addresses the impact of TK on system governance, other ECE providers, workforce preparation and compensation, professional development, funding, and program evaluation.