I have a question about this.
> There would be little use, for example, in
> teaching about a subordinate conjunction like 'unless' before kids are
> developmentally ready to handle it (I understand that 'unless' comes in
> rather late).

Are there any texts for native speakers which teach
unless?  If so, what do they say about it?  The only thing that I would
think a native speaker would need to know about unless is that it is a
subordinate conjunction.

On the other hand, I can imagine reasons for teaching the following.

> Yet early-grade grammar materials are filled
> with worksheets and multi-choice tests that ask children to
> supply/choose the correct verb form, plural form, etc. What are these
> worksheets trying to do?

Even in Oakland, the goal of teaching about a non-standard dialect of
English was
to have students control (a deliberately vague term here) standard
English.
I could not agree more with Johanna.

> For kids from
> nonstandard-dialect backgrounds, the worksheets are sending the message
> that their language is wrong, since they are likely to pick a wrong
> answer a lot of the time. There is no context explaining that the
> (written) language of school might be different from the language they
> are used to; there is no consideration of the fact that children in the
> same class from different backgrounds will be challenged differently by
> such materials.

The very nature of school introduces students to other dialects of
English.  A much better strategy would be designing exercises around
recognition of those dialects.  Although I can cite no research, I
suspect that almost all kids arrive in school knowing that there is
social language variation: older people speak differently than younger
people.  We need material which exploit that knowledge.

I think there is a better explanation for the following.

> In general, language arts materials mostly ignore the vast store of
> subconscious grammar knowledge children bring with them to school. This
> is, I believe, because the people who write grammar materials either
> don't know about this knowledge or don't
> want to pay any attention to it in developing their materials.

Most classroom teachers do not know this information because there own
experiences with learning about language don't expose them to this
perspective.

Bob Yates, Central Missouri State University