Do you have to know a second language to teach a second language?

I finally received my AmeriCorps placement...I will be serving as an English as a Second Language (ESL) Instructor! My supervisor has been teaching ESL for 15 years, 8 of those spent in Brazil so I think I'm in good hands! I've been assigned to the super beginner class, which is people who really know little to no English. This is going to be quite a challenging experience since I've never really taught...well anything even though I just spend two years and $50k on a degree in education. I also applied for a couple of online programs to get either a degree or a graduate certificate to certify me to teach English so I'll be able to learn as I go. That's the thing I think is so great about AmeriCorps...there is no way I could go out and get a position as an ESL teacher in the real world since I have no experience in the field, but with AmeriCorps I have the opportunity to try this whole new career path that I might never have been able to to otherwise. It's going to be such a challenge, but it's a challenge I'm really excited about. Wish me luck!