I think that working with and observing ESL students can teach us a great deal
about how to help non-ESL students become better writers. This applies not only to
issues of verb tense and historical linguistics, but also to the importance of
teaching grammar in college level freshman composition classes. In listening to
lectures from my colleagues who are linguists, I find that many of them use the
intrinsic-extrinsic nature of grammar as evidence in support of the argument that
formal grammar instruction, though useful in ESL classes, is worthless in
composition classes.  Yates points out that we can profit from the opposite
argument -- that demonstrating these intrinsic-extrinsic grammars can help our
students become better writers.

Bob Yates wrote:

> Teaching non-native speakers has made me realize how much knowledge of
> English native speakers "get for free."  Our discussion about the
> English tense aspect system has been about how to explain it.  Given its
> complexity, it is remarkable the few kinds of non-standard forms that
> occur in the various dialects of native speakers. I suspect the kind of
> tense problems in native speaker writing that teachers are responding to
> deal with changes from the past to the historical present to relate a
> story in more immediate, vivid terms.  In other words, even these
> non-standard switches in tense are principled.
>
> As a teacher of pre-service teachers, I think it is much better to show
> my students how much complex knowledge we all have about English which
> is never taught. Variability occurs because certain principles of
> English are in conflict and/or the writing system is an imperfect
> representation of what is possible in the oral language.