The first day of school on many Bay Area campuses was yesterday, marking the first time in more than a century that a new grade level -- transitional kindergarten -- is being offered to some students.

Transitional kindergarten was created by the Kindergarten Readiness Act, authored by state Sen. Joe Simitian, D-Palo Alto, and signed

by then-Gov. Arnold Schwarzenegger in September 2010.

The legislation targets children who are too young to enter regular kindergarten and changed the minimum age a student can enter kindergarten.

The two-year program does not involve bringing new, younger students into classes, but rather it accommodates students born between the

old kindergarten cutoff date, Dec. 2, and the new cutoff date, which is being moved up a month at a time over the next three years to Sept. 1.

Transitional kindergarten will feature a more age-appropriate curriculum for that first year before the students move on to regular kindergarten the second year.

An estimated 40,000 students around the state will be offered the transitional kindergarten curriculum this year, and eventually about 125,000 children will be eligible once the program is fully phased in by 2015.

The new grade level is the first in California since 1891, according to Simitian, who said in a statement that transitional kindergarten "will get kids off to a strong start at no additional cost to the state.