Hi Katie159,
I've interviewed for several different kinds of teaching positions and the main thing that surprised me was that almost all of my interviews were conducted in Spanish. As soon as the interviewer knew I was a native English speaker he or she wasn't concerned about testing my English skills. You don't mention how good your Spanish is, but I would try practicing interviews in Spanish just in case. Otherwise, all of my interviews were very straight forward: how much experience (side note: I had basically zero when I started), how long I was staying in Argentina, why I wanted to be here, etc. Of course, this is just my experience and other people may have different opinions.
Mucha suerte and let me know if you have any other questions!