S.D. Codified Laws § 32-12A-12
A commercial learner's permit may be issued to a person eighteen years of age who holds a valid operator's license.
No commercial learner's permit may be issued for a period to exceed one year. No commercial learner's permit may be renewed without the holder having to retake each general and endorsement knowledge test. A score for a successfully completed segment of the skills test is only valid during initial issuance of the commercial learner's permit. If the permit is renewed, the person shall retake each segment of the skills test. A commercial learner's permit holder is not eligible to take the skills test in the first fourteen days after initial issuance of the permit.
The holder of a commercial learner's permit may, unless otherwise disqualified, drive a commercial motor vehicle only if accompanied by the holder of a commercial driver license with the proper class and endorsements necessary to operate the commercial motor vehicle, who is twenty-one years of age, and is at all times physically present in the front seat of the vehicle next to the permit holder or if in a passenger vehicle directly behind the driver, and at all times has the permit holder under observation and direct supervision for the purpose of giving instruction in driving the commercial motor vehicle.
SDCL 32-12A-12