The Board of Educational Lands and Funds shall cause school land to be classified for rental purposes (1) at least once each five years, (2) each time that the land is leased or that an assignment of a lease is made, and (3) when the board deems it to be in the best interest of the state. The leasing of the land shall be regulated by sections 72-232 to 72-239. When a lease is offered for sale, the new rental shall be made public. When the board has ordered the reclassification of any of the school lands in any county, it shall prescribe the method and promulgate rules governing the classification of educational lands. It shall have a classification of all the educational lands in the county prepared by a competent person, who shall make a detailed field examination of each forty-acre tract of educational lands for the purpose of obtaining information as to the type and rating of the soil, its adaptability, the topographical character of the land, and the location and number of acres of each type. His or her report of such field examination shall be prepared in the form of a detailed map with complete explanations and shall be filed with the board. The board may employ private appraisal firms to aid it in determining the value of educational lands.