TK or Preschool? Weighing the Year Before Kindergarten on the Peninsula

A child who turns 4 in the Bay Area now has an option that families didn't have a few years ago. California finished rolling out universal transitional kindergarten (TK) in the 2025-26 school year, and the choice between TK and private preschool is a live one for many Peninsula households.

What TK is

KTVU reported that districts must now offer TK to every child who turns 4 by September 1 of the school year. TK is a play-based program with a focus on math and literacy, and it is free. The state requires one adult for every 10 students.

More than 177,000 children were enrolled in TK the previous year, roughly 50% to 60% of eligible children statewide, according to the same report. Enrollment has been growing by 20,000 to 30,000 children a year.

Who is eligible

Eligibility depends on birthday:

• Children who turn 4 by September 1 qualify in the school year that starts that fall
• Children with later birthdays aren't eligible for TK that year and may wait or attend preschool
• Each district runs its own enrollment, so timing and sites vary

A family in San Carlos and one in Redwood City might fall under different districts with different start dates and class locations.

Preschool before TK

TK covers one year. The years before it, from age 2 or 3, are served by private preschools, family child care homes and subsidised programs. The San Mateo County needs assessment found that preschool is the best-served age group in the county, with 94% of demand met in 2022 and about 1,107 spaces short.

For younger children, supply is tighter. The same report found only 34% of infant and toddler demand was met.

Comparing the options

Palomar College's summary of California's Title 22 rules gives the 1:12 ratio for children aged 2 to 5 with a fully qualified teacher in a typical licensed center.

Day length matters

Many working families find that a school-day schedule doesn't cover their work hours. KTVU's report doesn't give TK program hours, so parents should ask their district. Families who need a longer day often combine TK with before- and after-school care, or choose a center that covers the full day.

One parent quoted in KTVU's coverage said TK saves her about $1,000 a month in daycare costs. That's one family's figure and depends on the alternative she would have used.

Aftercare and the gap between TK and work hours

Families who choose TK still need a plan for the hours outside the school day. Options include before- and after-school programs run by the district or a community provider, a family child care home or a nanny share. The county assessment found school-age care is the tightest of the three groups it measured, with about 10,260 spaces short, so aftercare can be harder to find than a preschool place.

That's worth checking before committing to TK, since the free program only helps a family if the surrounding hours are covered.

Questions to ask each option

1. How many hours does the day cover, and what happens outside them?
2. What is the staff-to-child ratio in practice?
3. How are transitions to kindergarten handled?
4. What happens if a child's birthday falls near the cut-off?

What the county data adds

The San Mateo County assessment found that 94% of preschool demand was met in 2022. TK has since expanded, and the state's completion of the rollout in 2025-26 may change where 4-year-olds enrol. The assessment predates that change, so its preschool figures show the market before universal TK. Centers may have seen shifts in their 4-year-old enrolment since.

A note for families near the cut-off

A child with a summer birthday can be among the youngest in TK or among the oldest in preschool. Parents can talk with a teacher or the district about readiness. Families exploring a san carlos preschool for the year before TK can ask how a center works with children who are headed to TK in the fall.

The practical step is to check the district's TK enrollment dates, since they often open months before the school year.