No school district shall pay any teacher less than the state minimum salary. Provided, however, that school districts are authorized to reduce the state minimum salary by a pro rata daily amount in order to comply with the school district employee furlough provisions of Section 37-7-308. From and after July 1, 2012, no school district shall receive any funds under the provisions of this chapter for any school year during which the aggregate amount of local supplement as defined in Section 37-151-5 shall have been reduced below such amount for the previous year. However, (a) where there has been a reduction in adequate education program allocations for such district in such year, (b) where there has been a reduction in the amount of federal funds to such district below the previous year, or (c) where there has been a reduction in ad valorem taxes to such school district for the 1986-1987 school year below the amount for the previous year due to the exemption of nuclear generating plants from ad valorem taxation pursuant to Section 27-35-309, Mississippi Code of 1972, the aggregate amount of local supplement in such district may be reduced in the discretion of the local school board without loss of funds under this chapter. No school district may receive any funds under the provisions of this chapter for any school year if the aggregate amount of support from ad valorem taxation shall be reduced during such school year below such amount for the previous year; however, where there is a loss in adequate education program allocations, or where there is or heretofore has been a decrease in the total assessed value of taxable property within a school district, the aggregate amount of such support may be reduced proportionately. Nothing herein contained shall prohibit any school district from adopting or continuing a program or plan whereby teachers are paid varying salaries according to the teaching ability, classroom performance and other similar standards.