The board of education in each town shall consist of three, six, nine or twelve residents of such town, except as provided in § 9-205. In a town holding annual elections one-third of the members of such board shall be elected annually for the term of three years. Any town may, at any time, by ordinance, make the number of its board of education three, six, nine or twelve, and, at the next election thereafter held in each such town, the terms of all members of the board of education shall terminate and sufficient members shall be elected to fill the entire number of positions on said board as determined by such ordinance. In each such town which holds annual elections, at such next election one-third of the members of such board shall be elected for a term of one year, one-third shall be elected for a term of two years and one-third shall be elected for a term of three years; and at each annual election thereafter held, one-third of the members of such board shall be elected for a term of three years. In each such town which holds biennial elections, at such next election and at each biennial election thereafter held, members of the board of education shall be elected in accordance with the procedure prescribed in § 9-206 for a town which adopts biennial elections. The provisions of this section and § 9-204 shall not be construed to repeal or affect any special act relating to a town which elects the members of its board of education in a different manner or for different terms.