A School Swap

John was really interested in seeing just how far he could push the swaps. He walked the rest of the way to school on auto-pilot, and barely acknowledged Karyn when she tried to attract his attention from across the hall.
It wasn't until he'd sat down in his first class (eargh Maths with Mr Fenton) that he realized there was a buzz rippling through the room. Stood at the front of the class was a fashionably yet smartly dressed young woman.

She waited till she had there full attention then said "My Name is Miss Park, and I'll be your substitute teacher. As unfortunately several of your teachers Mr Fenton included have come down with really nasty food bug.I'm sure you'll all join with me in wishing them a speedy recovery"
John's attention drifted off at that point as his brain was suddenly afire with possibilities of swapping this teacher with one of his fellow students. All he had to do was work out who.
Just then the door began to open. Perfect a latecomer, John thought, I could swap them while they're both at the front and then sit back and see how it plays out. He concentrated on Miss Park and then on the latecomer as they walked in.
John nearly burst out laughing when he saw who it was.