California Code, Education Code - EDC § 44919

(a) Governing boards of school districts shall classify as temporary employees those persons requiring certification qualifications, other than substitute employees, who are employed to serve from day to day during the first three school months of any school term to teach temporary classes not to exist after the first three school months of any school term or to perform any other duties which do not last longer than the first three school months of any school term, or to teach in special day and evening classes for adults or in schools of migratory population for not more than four school months of any school term.  If the classes or duties continue beyond the first three school months of any school term or four school months for special day and evening classes for adults, or schools for migratory population, the certificated employee, unless a permanent employee, shall be classified as a probationary employee.  The school year may be divided into not more than two school terms for the purposes of this section.

(b) Governing boards shall classify as temporary employees persons, other than substitute employees, who are employed to serve in a limited assignment supervising athletic activities of pupils;  provided, such assignment shall first be made available to teachers presently employed by the district.  Service pursuant to this subdivision shall not be included in computing the service required as a prerequisite to attainment of, or eligibility to, classification as a permanent employee of a school district.

(c) In any district, the governing board may, to prevent the stoppage of school district business when an actual emergency arises and persons are not immediately available for probationary classification, make an appointment to a position on a temporary basis for a period not to exceed 20 working days.  The person so appointed shall be deemed to be a temporary employee who is employed to serve from day to day.  Service by a person in such an appointment on a temporary basis shall not be included in computing the service required as a prerequisite to attainment of, or eligibility to, classification as a permanent employee of a school district.