Don't present to the "whole class"... talk to them one at a time... from the front of the room.
Seriously, run a pattern in the back of your head, making a point to look at every person in the room as you speak. Between remembering what the hell you are talking about and trying to run the subroutine, your little lizard brain will be too busy to freak out.
It works for me anyway.
Good luck!