Originally Posted by WhamATC

Mary Jo Dupey is a vocal coach.
Katie Agresta is a vocal teacher.

Vocal teacher teaches you how to sing better, makes you be able to hold notes and hit higher ones, vocal exercises, etc.

Vocal coaches are more about stage looks, how to perform better on stage (not really in terms of voice), etc.

He needs Katie Agresta.
Mary Jo Dupey is for the concert itself really not voice.