The cutoff birthday will be September rather than December. The idea is to make sure 4 year olds aren't in kindergarten.
"California was one of the few state where kids were still 4 years old going into kindergarten, and often they didn't have the maturity and the skills they needed to really succeed," said Deborah Kong of Preschool California, a transitional kindergarten proponent.
While they wait, 4 year olds can attend transitional kindergarten, known as TK. It will be part of California's public school system next fall, the first grade added since 1891.
Some schools have already tried it.
"TK has been proven to be valuable to the school districts in lowering retention, special ed placement and we predict dropout rates will go down," said Cathy Wietsock of the Orange County Department of Education.
But some school districts are concerned about the costs. While the state gives them money for each child that attends, whether it's TK or regular kindergarten, participation is voluntary and each school may not have enough students.
"Perhaps three from one location, four from another, maybe five from another location, and try to serve them in one location could be a real challenge for some areas throughout the state," said Jeff Bell of School Services of California.
Even past the cutoff date, parents who believe their child is ready for kindergarten can ask for early admission.