Upon the establishment of a new school district of the first class having within its boundaries a city with a population of four hundred thousand people or more, the directors of the largest former first-class district and three directors representative of the other former first-class districts selected by a majority of the board members of the former first-class districts and two directors representative of former second-class districts selected by a majority of the board members of former second-class districts shall meet at the call of the educational service district superintendent and shall constitute the board of directors of the new district. Each board of directors so constituted shall proceed at once to organize in the manner prescribed by law and thereafter shall have all the powers and duties conferred by law upon boards of first-class districts, until the next regular school election and until their successors are elected and qualified. Such duties shall include establishment of new director districts as provided for in *RCW 28A.315.670
. At the next regular school election seven directors shall be elected by director districts, two for a term of two years, two for a term of four years and three for a term of six years. Thereafter their terms shall be as provided in *RCW 28A.315.460
Vacancies once such a board has been reconstituted shall not be filled unless the number of remaining board members is less than seven, and such vacancies shall be filled in the manner otherwise provided by law.