Mo. Rev. Stat. § 302.080: Exemptions from license law.

The following persons are exempt from license hereunder:

(1) Any person while operating any farm tractor or implement of husbandry temporarily operated or moved on a highway;

(2) A nonresident who is at least sixteen years of age and who has in his immediate possession a valid license issued to him in his home state or country;

(3) A nonresident who is at least eighteen years of age and who has in his immediate possession a valid license issued to him in his home state or country which allows such person to operate a motor vehicle in the transportation of persons or property as classified in section 302.015;

(4) Convicted offenders of the department of corrections who have not been convicted of a motor vehicle felony as follows driving while intoxicated, failing to stop after an accident and disclosing his or her identity, or driving a motor vehicle without the owner's consent may operate state-owned trucks for the benefit of the correctional facilities, provided that such offender shall be accompanied by a correctional officer or other staff person in such truck.