Who is Keith Carter from An Abundance of Katherines and what is their importance?

Keith Carter is Colin's tutor. Colin nicknames him Krazy Keith. Keith starts as Colin's tutor when Colin is in third grade. Colin goes to school for three hours per day and then spends the rest of the school day with Keith in Keith's office. Keith has a wife and a daughter. Keith's daughter is about eight months older than Colin and her name is Katherine.