Here are some of the Ed code citations covering school libraries in California:

California Education code

Section 18100. The governing board of each school district shall provide school library services for the pupils and teachers of the district by establishing and maintaining school libraries or by contractual arrangements with another public agency.

18120. The governing board of a school district maintaining its own library or libraries may appoint a librarian or librarians to staff the libraries provided they qualify as librarians pursuant to Section 44868.

44868. No person shall be employed as a library media teacher in any elementary or secondary school, unless he or she holds a valid credential of proper grade authorizing service as a library media teacher or a valid teaching credential issued by the Commission on Teacher Credentialing if he or she has completed the specialized area of librarianship.

44869. Any library media teacher when employed full time as a library media teacher or serving full time, partly as a library media teacher and partly as a teacher, shall rank as a teacher.

Here is the Commission on Teacher Credentialing website about school librarians:

http://www.ctc.ca.gov/codcor.doc/000013/000013.html

See especially:

(2) Nothing in this section shall be construed to preclude local governing boards from employing non-credentialed individuals to assist in the provision of library services, provided that the employment of non-credentialed personnel is not intended to supersede the requirement to include holders of the Library Media Teacher Services Credential or other credential authorizing library service pursuant to Education Code 44868 in the coordination and implementation of public school library programs. Services provided by non-credentialed personnel shall not include those activities requiring possession of a valid Library Media Teacher Services Credential, as specified in Subsection (b) of this section.

(b) Authorization. The Library Media Teacher Services Credential authorizes the holder to instruct pupils in the choice and use of library materials; to plan and coordinate school library programs with the instructional programs of a school district; to select materials for school and district libraries; to coordinate or supervise library programs at the school, district or county level; to plan and conduct a course of instruction for those pupils who assist in the operation of school libraries; to supervise classified personnel assigned school library duties; and to develop procedures for and management of the school and district libraries.