Cal. Education Code § 44959.5

(a) The layoff provisions of Sections 44955, 44956, 44957, 44958, and 44959 shall not be applicable to probationary certificated employees who are covered by a collective agreement which contains provisions for the layoff and reassignment of such employees. (b) If layoff proceedings are commenced under procedures prescribed by any of the sections referred to in subdivision (a), such proceedings shall continue in accordance with the statutory procedures, notwithstanding the subsequent adoption of a collective agreement or the inclusion in the coverage thereof of employees not so covered at the time such proceedings commenced. (c) If layoff proceedings are commenced under a collective agreement which contains provisions for the layoff of probationary certificated employees, such proceedings shall continue in accordance with the agreement, notwithstanding the subsequent termination of the agreement. (d) This section shall only apply to a school district in which the average daily attendance is 250,000 or more and shall not be interpreted to apply to the termination of any probationary certificated employee pursuant to Section 44948 or 44949.