The members of the board elected at the formation election shall at their first meeting classify themselves by lot into two classes as nearly equal in number as possible. The term of office of the class having the greater number shall expire at the commencement of the regular meeting of the board in April following the next general March election; and the term of office of the class having the lesser number shall expire at the commencement of the regular meeting of the board in April following the next general March election thereafter.