Cal. Education Code § 44903

On the unionization, unification, uniting, or consolidation of one or more school districts in which the average daily attendance for the preceding school year was less than 250 pupils, with a district or districts in which the average daily attendance was or, as a result of the unionization, uniting, consolidation, or unification, becomes 250 or more pupils, the regular three-year probationary period required of certificated employees for permanent status by Section 44882 shall be deemed to have commenced at the beginning of the employee’s first complete year of consecutive employment by the school district having an average daily attendance of less than 250 pupils. Every certificated employee who has been employed for three or more complete consecutive school years by a district having an average daily attendance of less than 250 pupils shall, immediately upon his employment in a certificated position following such unionization, unification, uniting, or consolidation, be a permanent employee. The amendments to this section enacted by the Legislature at the 1977–78 Regular Session shall apply only to the unionization, unification, uniting, or consolidation of school districts which becomes effective for all purposes on or after January 1, 1979.