To take a leaf out of Michael Lachance's book, Land Your Dream Job:
"What does business casual mean exactly?
Business casual does not mean dressing casually as the name may sound.
Some may think business casual means wearing a casual outfit (say jeans and a collared shirt), but it really means dressing down a business outfit (suit pants with no tie).
The goal is to look professional, put together, and neat."
At the end of the day, we want everyone to feel relaxed, happy, and ready to learn.
Wear what makes you comfortable :)