(a) The duration of a designation as mentor teacher shall normally be for a period of three consecutive years. Designations having a duration of less than three years shall be one or two years only and may be renewed by the governing board, without review and renomination, until the three-year maximum is reached.

(b) Except in school year 1983-84, proration of the mentor teacher annual stipend shall occur only when nonprogrammatic circumstances, such as extended absence for health reasons, prevent the mentor teacher from completing the designated mentorial period.

(c) If for any reason a mentor is unable to complete the designated mentorial period, the governing board may select a replacement from committee-nominated alternates, if any.