What Is TK? Transitional Kindergarten Explained (Age, Ratios, Cost)

Reviewed and updated October 2026 against California Education Code section 48000 and the California Department of Education TK FAQ.

TK at a glance

What does TK mean in school?

TK means transitional kindergarten. California Education Code section 48000 defines it as “the first year of a two-year kindergarten program that uses a curriculum that is age and developmentally appropriate”. In practice that means a classroom in a public elementary school, with a credentialed teacher, where 4-year-olds learn through play, structured activities and early literacy and math, aligned to the state’s California Preschool/Transitional Kindergarten Learning Foundations.

So TK is not a separate grade with its own standards in the way first grade is. It is the first half of a two-year path through kindergarten, designed for children who are a year younger.

What age is TK?

From the 2025-26 school year onward, California law says a child who will have their fourth birthday by September 1 “shall be admitted” to TK. In other words, TK is now open to every 4-year-old in the state. Children who turn 5 by September 1 go to kindergarten instead.

TK eligibility widened step by step over the previous decade:

That history is why older guides describe TK as a program only for children with fall birthdays. That was true before 2022; it is no longer the rule.

TK vs preschool vs kindergarten

For the full picture of ages before school, see what age preschool is, and for every grade after, our US school grades by age chart.

What happens in a TK classroom?

The law requires a curriculum that is “age and developmentally appropriate” and describes it as a “strengths- and play-based approach to joyful, engaged learning”. A typical TK day mixes:

• Play-based learning: centers for building, art, pretend play and early science.
• Early literacy: stories, letter sounds, rhymes and writing names.
• Early math: counting, shapes, patterns and comparing quantities.
• Social and emotional skills: taking turns, following routines, managing feelings and making friends.
• Movement and outdoor time, plus meals and rest built into the school day.

The aim is to get 4-year-olds ready for kindergarten without pushing kindergarten work a year early.

Class sizes, ratios and teachers

Section 48000 sets rules that schools must meet to receive state TK funding:

• Class size: an average TK class enrollment of no more than 24 pupils at each school site.
• Adult-to-child ratio: at least one adult for every 12 children from 2022-23, tightened to at least one adult for every 10 children from 2025-26.
• Teacher qualifications: credentialed teachers first assigned to TK after July 1, 2015 must also have, by August 1, 2025, at least 24 units in early childhood education or child development, comparable classroom experience with preschool-age children, or a child development teacher permit or early childhood education specialist credential.

That is why a TK room usually has a teacher plus an aide or assistant: with 20-plus children, a second adult is needed to meet the 1-to-10 ratio.

Should your child do TK?

TK is optional, and families decide based on their child. Things worth weighing:

• Your child’s readiness for a school setting: a school-day schedule, routines and a larger group.
• Your current care arrangement: TK is free, which can replace paid preschool or childcare for a year.
• Hours: TK follows the school’s schedule, so check the day length and whether before- or after-school care is available.
• The school itself: visit the classroom and ask about class size, the adults in the room and how the TK and kindergarten teachers work together.

Children who skip TK simply start kindergarten at 5, as they would have before TK existed.

How to enroll in TK

• Check your child’s birthday against the September 1 cutoff for the year you want to start.
• Contact your local public elementary school or school district; TK enrollment usually opens alongside kindergarten enrollment in the winter or spring before the school year.
• Have proof of age, proof of address and immunization records ready, as you would for kindergarten.
• Ask whether your neighborhood school runs TK on site or at another school in the district.

Frequently asked questions

What does TK stand for in school?

TK stands for transitional kindergarten. In California law it is the first year of a two-year kindergarten program, for children who are 4 at the start of the school year.

What age is TK?

In California, from the 2025-26 school year on, a child who turns 4 by September 1 must be admitted to TK. Most children start TK at age 4 and move to kindergarten the following year at age 5.

Is TK the same as preschool?

No. TK is part of the public school system and is run by school districts and charter schools, with credentialed teachers and state rules on class size and adult ratios. Preschool is run by many kinds of providers, public and private, under different rules.

Is TK mandatory in California?

No. Families choose whether to enroll, and a child can go straight to kindergarten at 5. What the law requires is on the school side: districts and charter schools running TK must admit every child who turns 4 by September 1.

How many kids are in a TK class?

California law requires schools to keep an average TK class enrollment of no more than 24 pupils per school site, with at least one adult for every 10 children from 2025-26.

Is TK free?

Yes, as part of public education. TK is offered by public school districts and charter schools, which receive state funding for TK students.

Do kids have to do TK before kindergarten?

No. A child can skip TK and start kindergarten at 5. TK is an optional extra year for 4-year-olds.

Do other states have TK?

California is where “transitional kindergarten” is defined in state law and now open to every 4-year-old. Other states and districts run programs for 4-year-olds under different names, most often pre-K, with their own rules.