How do they teach then? Are they teaching students who already have some English knowledge? Your friends are helping them improve, instead of teaching from scratch? Its understandable if thats the case.
Second language acquisition beyond entry level should be in the target language. There are methods ( http://www.everythingesl.net/inservices/language_stages.php is a quick example ) that require no actual native language knowledge on the part of the teacher.
I haven't taught a second language myself, but I am around a few people who teach or have taught languages, and I've picked up on it a bit.
Most of the times they have some prior background in the language. But often you teach to very young kids as well, in that case you are usually paired with a local teaching assistant.
