How do people receive an assignment in The Giver?

In Jonas' world, there is a Ceremony every year in December during which the children are given different privileges (like riding a bike) or status signifiers (like a two button jacket), depending on their "age".  It is during The Ceremony of Twelve that each child is told what their assignment will be.  The assignments are determined by The Elders, who closely observe the child for several years before the time of the Ceremony of Twelve in order to find the best fit for their assignment.