Cal. Educ. Code § 51511

Nothing in this code shall be construed to prevent, or exclude from the public schools, references to religion or references to or the use of religious literature, dance, music, theatre, and visual arts or other things having a religious significance when such references or uses do not constitute instruction in religious principles or aid to any religious sect, church, creed, or sectarian purpose and when such references or uses are incidental to or illustrative of matters properly included in the course of study.