Who is Mr. McGrath from After Ever After and what is their importance?

Mr. McGrath, Jeffery's gym teacher, is also his math tutor. Jeffery is struggling with both math and his self-confidence when he begins the math tutoring. He doesn't really like Mr. McGrath who has the personality of a military drill sergeant but it's Mr. McGrath who gives Jeffery a level of confidence he'd been lacking by pointing out that Jeffery has accomplished a great deal in gym class.