Mo. Rev. Stat. § 164.201: Exchange and sale of refunding bonds — restrictions.

No refunding or renewal bond shall be exchanged by the board of any school district for any outstanding bond for a sum less than ninety cents on the dollar of its face value. The board also may sell the refunding or renewal bonds for cash if in its judgment it will be to the interest of the school district; but no commission shall be allowed or cost incurred in the exchange or sale of bonds which will reduce the net proceeds of the same to a less amount than ninety cents on the dollar, and all sums of money realized from the sale of refunding or renewal bonds shall be used in the redemption of outstanding bonds of the school district.