Whenever the board has purchased the bonds of any city, county, or municipality, approved by the attorney general, the certificate of the attorney general attesting their validity shall be admitted and received as prima facie evidence of the validity of the bonds; and in all cases in which the proceeds of the sale of these bonds have been received by the proper officers of the city, municipality, or county, or by the party acting for them in negotiating the sale of the bonds, the city, municipality, or county is thereafter estopped from denying the validity of the bonds and they shall be held to be valid and binding obligations. In the case of any bonds bought under this section, premium or discount shall be distributed over the life of the bonds.
Tex. Educ. Code § 66.04