Cara seemed outwardly amused by the question. Her fingers stopped fiddling with her sleeve while thought about it. Then she gave the most genuine smile she'd given to a student before. 

"Telling everyone to wear 'whatever' seems a little risky," she said. "Wear casual clothes." Then the bell rang. It had barely even finished echoing around the room before Cara had scraped her chair back, fathered up her things and hurried out of the room, calling "See you later!" Over her shoulder to her classmates. Truth be told, Cara had barely even noticed the time go by and was sure she had learnt nothing in that lesson. She hurried to the next, counting down the seconds until she could go home and begin preparations for the party.