Cal. Education Code § 44918

(a) Any employee classified as a substitute or temporary employee, who serves during one school year for at least 75 percent of the number of days the regular schools of the district were maintained in that school year and has performed the duties normally required of a certificated employee of the school district, shall be deemed to have served a complete school year as a probationary employee if employed as a probationary employee for the following school year. (b) Any such employee shall be reemployed for the following school year to fill any vacant positions in the school district unless the employee has been released pursuant to subdivision (b) of Section 44954. (c) If an employee was released pursuant to subdivision (b) of Section 44954 and has nevertheless been retained as a temporary or substitute employee by the district for two consecutive years and that employee has served for at least 75 percent of the number of days the regular schools of the district were maintained in each school year and has performed the duties normally required of a certificated employee of the school district, that employee shall receive first priority if the district fills a vacant position, at the grade level at which the employee served during either of the two years, for the subsequent school year. In the case of a departmentalized program, the employee shall have taught in the subject matter in which the vacant position occurs. (d) Those employees classified as substitutes, and who are employed to serve in an on-call status to replace absent regular employees on a day-to-day basis shall not be entitled to the benefits of this section. (e) Permanent and probationary employees subjected to a reduction in force pursuant to Section 44955 shall, during the period of preferred right to reappointment, have prior rights to any vacant position in which they are qualified to serve superior to those rights hereunder afforded to temporary and substitute personnel who have become probationary employees pursuant to this section. (f) This section shall not apply to any school district in which the average daily attendance is in excess of 250,000.