What I’m teaching is considered EFL, or English as a Foreign Language, as opposed to ESL, or English as a Second Language. The difference is in the context: English instruction outside of an English-speaking country is EFL, inside an English-speaking country it’s ESL. Both fall under the umbrella of Teaching English to Speakers of Other Languages (TESOL).
The benefit of being a teacher of EFL is that you have the opportunity to live in another country and experience a different culture. But as far as the actual teaching goes, EFL is a tougher assignment. Generally, people who are learning English in an ESL setting are motivated to learn; they are either immigrants who know that they need English to have a better life, or they are students in an immersion environment in which they need English for their day-to-day survival. Another benefit of ESL is that you often get a mix of first languages in the classroom, so that in order to communicate with eachother, the students have no choice but to speak English. Therefore, the teachers expends less energy fighting to keep the class on task.
In the EFL situation, however, the majority of students do not have an internal motivation to learn English. They are in English class because their parents want them to be, because their school or university requires it, or because their employer thinks they need it. And this lack of internal motivation can translate into a lack of enthusiasm. Furthermore, they all speak the same first language, so since they often aren’t that motivated to practice English in the first place, they’ll retreat to the first language at every opportunity.
I think that foreign language learning brings out the worst in students this way because they’re required to be active learners in class. They might have to take Introduction to Astonomy to satisfy a requirement, but at least they can sit in the back of the lecture hall and doze off. In language class, however, they’ll have to actually do something, like practice a conversation with a partner, walk around and take a survey of their classmates, write something on the board, or perform a skit in front of the class. And they’ll be expected to do it all in a language that they can hardly speak, so they’re certainly not going to be looking very cool (or here in Mexico, very macho) in the process.