Younger preschoolers (babies and ones) should be promoted to the next class based on their level of physical development. For example, an infant should go to the crawler class when he or she is proficient at crawling.
When a child begins walking he or she moves to the walker class or ones class. (The children should move only as long as space allows and an appropriate child-teacher ratio is maintained.)
Twos, threes, fours, and kindergartners promote to a new department or class at the beginning of the Sunday School year and remain in the same class or department until the next promotion day.