In my class we are discussing teaching English as a second language. Some contend that to teach ESL, we need to know the processes and theories about first language acquisition, but it is not clear to me why or whether this helps. Is there clear evidence that this knowledge helps?
Case in point: I know several ESL teachers that volunteer and are great teachers and know nothing of these theories. On the other hand, to draw a parallel, in the code-switching literature there is plenty of evidence that: teachers that know what code-switching is about get their students to perform better in writing and reading exams. (for example: Rodolfo Jacobson and The Implementation of a Bilingual Instruction Model: The "New" Concurrent Approach.)
Is there hard evidence or at least a program that includes first lang. acquisition theories and the teaching of ESL?