Mo. Rev. Stat. § 162.1300

If a change in school district boundary lines occurs under section 162.223, 162.431, 162.441, or 162.451, or by action of the state board of education under section 162.081, including attachment of a school district's territory to another district or dissolution, such that a school district receives additional students as a result of such change, the statewide assessment scores and all other performance data for those students whom the district received shall not be used for three years when calculating the performance of the receiving district for three school years for purposes of the Missouri school improvement program.