20-6-507. Opening of middle school. The trustees of any elementary district may open a middle school when such opening has been approved by the superintendent of public instruction. The state superintendent shall investigate an application for the opening of a middle school and shall approve or disapprove the opening before the fourth Monday in June preceding the first year of intended operation. When a middle school opening is approved, the county superintendent shall estimate the ANB after investigating the probable enrollment for the middle school. The ANB so estimated shall be used for budgeting and BASE funding program purposes during the ensuing school fiscal year.