How to deal with pre-show jitters?

Before and during every lesson, I am perfectly fine. When it's show day I'm fine all the way up to about 20 minutes before my classes. It's not that I'm scared, it's just that I start to get butterflies in my stomach. I've been showing for over 10 years, and it still happens to me. I try taking deep breaths, and telling myself to relax, but nothing seems to work. Do you have any ideas of what I could do? Thanks