All school land shall be subject to lease at fair market rental as determined by the Board of Educational Lands and Funds. When the board deems it expedient to raise or lower the rental and the appraised rental valuation of school lands, the board shall adopt rental schedules according to classification and schedules of valuations for the counties involved. In arriving at such rental schedules, the board shall consider the rental of other lands similarly situated and any other relevant factors bearing upon the rental of such school lands. The fair market rental as determined by the board shall then be capitalized at an annual rate of four percent to compute the appraised rental valuation.