Whenever an election shall be held for the purpose of securing the approval of the voters for the formation of a new school district other than a school district of the first class having within its boundaries a city with a population of four hundred thousand people or more, if requested by one of the boards of directors of the school districts affected, there shall also be submitted to the voters at the same election a proposition to authorize the board of directors to divide the school district, if formed, into five directors' districts in first-class school districts and a choice of five directors' districts or no fewer than three directors' districts with the balance of the directors to be elected at large in second-class school districts. Such director districts in second-class districts, if approved, shall not become effective until the regular school election following the next regular school election at which time a new board of directors shall be elected as provided in *RCW 28A.315.550
. Such director districts in first-class districts, if approved, shall not become effective until the next regular school election at which time a new board of directors shall be elected as provided in *RCW 28A.315.600
, and 28A.315.620
. Each of the five directors shall be elected from among the residents of the respective director district, or from among the residents of the entire school district in the case of directors at large, by the electors of the entire school district.