California Code, Education Code - EDC § 45220

(a) “Common board” as used in this article means a board with identical members that governs more than one school district.  “Common administration” as used in this section means the administration by a person employed by governing boards of more than one district or a common board to act as chief executive officer for more than one school district.

(b) The term “a district whose average daily attendance is 3,000 or greater” shall be construed to include any district which is the only district under the jurisdiction of the county superintendent of schools regardless of its average daily attendance.  It shall also include districts governed by a “common board” or which use a “common administration,” as defined in this section.