Who is in charge of the ceremonies in The Giver?

The Chief Elder is in charge of the ceremonies. 

A Committee of Elders carefully observes the children when they are close to turning Twelve to determine what assignment they should get.  Then during the Ceremony of Twelve the Chief Elder describes the class and then each individual in it, in order of their birth.  Each child is given an assignment that will be his or her job for life. 

The Ceremony of Twelve is...

The Chief Elder is in charge of the ceremonies. 

A Committee of Elders carefully observes the children when they are close to turning Twelve to determine what assignment they should get.  Then during the Ceremony of Twelve the Chief Elder describes the class and then each individual in it, in order of their birth.  Each child is given an assignment that will be his or her job for life. 

The Ceremony of Twelve is the most important ceremony.  It takes place last, because the ceremonies go in order of the children’s ages.  At the Ceremony of Twelve, the Chief Elder recognizes the group and the individual.  This is rare, because usually individual differences are not acknowledged because the community does everything it can to enforce Sameness. 

The initial speech at the Ceremony of Twelve was made by the Chief Elder, the leader of the community who was elected every ten years. The speech was much the same each year: recollection of the time of childhood and the period of preparation, the coming responsibilities of adult life, the profound importance of Assignment, the seriousness of training to come. (Ch. 7) 

Jonas’s ceremony starts off normally.  Each child’s number is called, the little story told, and the assignment announced.  However, when Nineteen, Jonas’s number, is supposed to be called, the Chief Elder skips it.  Jonas is horrified.  He assumes he has done something wrong. 

She skipped me, Jonas thought, stunned. Had he heard wrong?  No. There was a sudden hush in the crowd, and he knew that the entire community realized that the Chief Elder had moved from Eighteen to Twenty, leaving a gap. (Ch. 7) 

Of course, the Chief Elder made no mistake.  Jonas was skipped to increase the community’s suspense, and to acknowledge the uniqueness of his assignment.  The Chief Elder announces that Jonas was selected, not assigned, as the Receiver of Memory.