Pretend like your sick, don't go to school, pretend like you can't talk, or you could kill your teacher(JUST KIDDING ON THAT LAST ONE!!!!) it's totally easy to get out of publically speaking in class.
Public speaking generally means speaking in front of an audience of more than one. Private speaking probably means a one to one conversation meant fro no-one else's ears.
One book I read recently...
Skip the day! That's what i would do.
If you do that, they'll be like, "hey! that kid didn't do anything yet!"
You're gonna have to sooner or later, so just make your's better than someone elses so...