An example might help. Here are two sentences:
- I don't see anything.
- I don't see nothing.
Now, in the class yesterday one of the pairs of sentences was this:
- Is there a Miss Smith in this office?
- Is it a Miss Smith in this office?
The students presented all sorts of contorted calculations attempting to construct different referential meanings for these two sentences. For example, the 'it' in the second dehumanizes Miss Smith; and so on. Not one of these students recognized that the second sentence is from African American English, and that it's referential meaning is the same as the first one. Not one. I should add that the students in this class were all "White," or rather, none of them belonged to the US hypodescent group labeled "Black."
This led me to wander a little off topic in the class, by questioning whether the lack of knowledge that White people typically have about Black people contributes to situations like what we see happening in Ferguson, etc. Of course, this little bit of AAE grammar is a little thing, almost inconsequential in itself, but not knowing lots of little things adds up to not knowing a lot.
And, why don't White people have this knowledge? Why is it that at no time in their "language arts" classes have these students been presented with facts about the linguistic variation that exists all around them? They've had to wait until they got to university, and then happened to take linguistics for one reason or another. And some of them are English Education majors, destined to themselves be language arts teachers.
The answer, it seems to me, is that we don't value what Black people know. To the extent that it differs from more mainstream English, their speech is just a broken, deficient form of that wider English. Nothing to see here; move along...