Testing Her Professor - C M Steele

She's not who she's pretending to be, and he knows it.
The question is...
What is he going to do about his little cheater?

He can't stop her from leaving the class without drawing attention, so he'll have to find another way to get her alone. Luckily, he has all the information at his fingertips, and soon he'll have a lot more in his hands.

This is a super short story about twin sisters switching places.