A regional manager interviewed me, one-on-one, on my college campus.
My recommendation is to show that you are really passionate about the cause, and research about City Year's core mission is before going into the interview. Showing that you have done the research and can reference parts of their mission statement will show your dedication.
Furthermore, I cannot stress this enough, but relax. My interview process with the regional manager ended up becoming more like a conversation than a formal interview.