The committee considers each child's interests and skills when giving them their life assignments.  The process actually appears to begin with the Eights, who are assigned volunteer hours, and inevitably gravitate to those jobs which suit their own interests and skills most closely.  This allows the committe to evaluate each child's performance for a few years in a practical situation before deciding on a life assignment for him or her. 

An examination of the assignments given to individual characters illustrates that the committee does indeed take into consideration individual aptitudes and abilities in their choices.  Father, who is quiet and patient, and was admittedly "drawn" to the children in the nursery, was given the job of Nurturer (Chapter 2), and Mother, who is very intelligent, was trained for "a prominent position at the Department of Justice" (Chapter 1).  Father remembers a friend named Andrei who spent all his free time with his construction set and was given the "Assignment of Engineer" (Chapter 2).  Among Jonas's peers, Asher, who is active and never serious, is chosen to be "Assistant Director of Recreation", and Fiona, who is sensitive, gentle, and calm, is assigned to be a "Caretaker of the Old" (Chapter 7).

What two factors did the committee consider for children's life assignments in The Giver?

Mainly, what we are told is that the committee looks at what the kids who were about to be twelves did in their volunteer time and also in their recreational time.

For example, we are told in Chapter 2 about the assingments of some of the friends that Jonas's dad had when he was younger.  The Elders watched him and saw that he spent his recreation time with a construction set.  They saw that all his volunteer hours were spent at building sites.  Because of that, they knew he should be an engineer.