Members of local school boards in districts having a population in excess of sixteen thousand shall reside in and be elected from single-member districts. Once, following every federal decennial census, the local school board shall divide the school district into a number of election districts equal in number to the number of members on the school board. Such election districts shall be contiguous and compact and as equal in population as is practicable; provided that the local school board of any district having a population of sixteen thousand or less may provide for single-member districts as provided in this section.