Members of the board of a district whose terms have not been staggered as of the date when this section becomes effective shall meet and classify themselves by lot into two classes as nearly equal in number as possible in order to determine when their respective terms shall expire. Unless otherwise provided in the bylaws, the term of office of the class having the lesser number of members shall be deemed to expire on the date for the general district election in 1969. The terms of the other members shall be deemed to expire on the date for the general district election in 1971.