Classes will be LARGE. The average class size in Chile in public and semi-public schools is about 40 students give or take 10. Combine this with the fact that this will be many of the students first exposure to a native speaker of English and you now have a frenzied level of excitement and enthusiasm among them. Come in friendly, but start the year very strict.  

What will my students be like?

There is no one answer to that question that could encompass the dynamics that you will encounter within the class. You will have angels and children that are very studious and do all the work. Others you will have to have to tell them to do work repeatedly. Chilean national pastime is soccer so all of your students will want to know who your favorite soccer team is. 

The type of students you have is directly related to where you're teaching.  The socio-economic demographic is one of the biggest factors is how much exposure your students have had to English.  Consider an IVY league prep school or an expensive private boarding school... consider the education standards.  Stereotypes are not always completely accurate but they do hold some truths.