Mo. Rev. Stat. § 543.210: Jury — number — selection.

If the case is thereafter tried before an associate circuit judge, the jury shall be composed of twelve persons, unless a less number shall be agreed upon, but not less than six. The selection of the jury and the practice and procedure relative to the jury in a case tried before an associate circuit judge shall be the same as in a case tried before a circuit judge except as otherwise provided herein.