At the next succeeding regular school election in a district where the number of directors has been increased from five to seven, and directors are elected at large, there shall be elected a director to succeed each incumbent director whose term is expiring in that year, and two additional directors. Upon organizing as required by section 279.1, either one or two of the newly elected directors who received the fewest votes in the election shall be assigned a term of two years as necessary in order that as nearly as possible one-half of the members of the board shall be elected biennially. If some or all directors are elected from director districts, the board shall assign terms appropriate for the method of election used by the district.