For the purpose of developing and maintaining vocational education facilities and programs to serve an area not exclusively within the boundaries of a single school district, the school districts serving such an area are empowered to affiliate with each other under such terms and conditions, not in conflict with this section and Section 59-53-1890, as they see fit. The affiliation shall be evidenced by a written instrument to be filed with the secretary and administrative officer of the State Board of Education and with the county boards of education concerned.