Dr. Lisa Green received her PhD from UM Amherst in formal syntax (the study of grammar from a theoretical standpoint that assumes that all langauges share the same universal structures). She then worked at Stanford with professors like Dr. John Rickford, who specializes in sociolinguistics, the study of language variation and change. She is now considered one of the foremost experts on the grammar of African American dialects, and she has published two major books on the subject: African American English: An Introduction and Language & the African American Child.
In this video, Dr. Green explains the systematic differences that these dialects have with Standard English and its social purposes. The talk was given at the University of North Carolina Chapel Hill, but it was organized with a popular audience in mind. She does a particularly good job of outlining problems with equating dialects with informal language and with demonstrating variation within Standard Englishes. She also offers a fairly comprehensive overview of the history of linguistic research surrounding this variety and advice for educators. Students, teachers, and other linguaphiles should watch this video: