As a cadet ages, he automatically moves up the the next patrol. However, he will not receive the equivalent Shield until all relevant Junior Requirements or Senior AC’s (Accomplishment Courses) requirements have been met.
Source: Officer’s Manual
Pages 15-24: Requirements by Patrol for Junior Cadets, 1st to 5th grade.
Pages 25-27 through 152: Rankings and Requirements for Senior Cadets/Adults, 6th grade and up.