You qualify for in-state tuition if you are the dependent of a nonresident active duty service member assigned to a duty station in Missouri. You keep the in-state rate as long as you stay continuously enrolled in an undergraduate or graduate degree program.
Give the admissions or registrar office at your Missouri institution a copy of your sponsor's orders assigning them to a duty station in Missouri, and proof that you are their dependent.
Your sponsor's orders assigning them to a Missouri duty station, your military dependent ID, and proof of your relationship to the service member.