California Code, Education Code - EDC § 87610

(a) The governing board shall give written notice of its decision under Section 87608 or 87608.5 and the reasons therefor to the employee on or before March 15 of the academic year covered by the existing contract. The notice shall be by registered or certified mail to the most recent address on file with the district personnel office. Failure to give the notice as required to a contract employee under his or her first or second contract shall be deemed an extension of the existing contract without change for the following academic year.

(b) The governing board shall give written notice of its decision under Section 87609 and the reasons therefor to the employee on or before March 15 of the last academic year covered by the existing contract. The notice shall be by registered or certified mail to the most recent address on file with the district personnel office. Failure to give the notice as required to a contract employee under his or her third consecutive contract shall be deemed a decision to employ him or her as a regular employee for all subsequent academic years.