If the driver holds an intermediate license, which occupants of the vehicle must wear seat belts?

According to Missouri law, if the driver holds an intermediate license, the driver and all passengers must wear a seat belt or suitable child restraint. If the driver holds a full driver license, the driver and front-seat passengers and all passengers under the age of 16 must wear a seat belt or use a suitable child restraint. However, all passengers should be suitably restrained even though Missouri law doesn't currently require it. Seat belts have been proven to save lives. [Use Seat Belts and Child Restraints, Chapter 8 – Safe Driving Tips for Everyday Driving, Missouri DOR Driver Guide]