A teacher's job is to teach and failure to correct a student's speech, just as failure to correct a math error, is a dereliction of duty. You might say, "Williams, Ebonics or black English is part of the cultural roots of black people and to disparage it is racism." That's utter nonsense. During the 1940s and 1950s, I lived in North Philadelphia's Richard Allen housing project, along with its most famous resident, Bill Cosby. We all were poor or low middle class but no one spoke black English. My wife was the youngest of 10 children. Listening to her brothers and sisters speak, compared to many of her nieces and nephews, you wouldn't believe they were in the same family. The difference has nothing to do with cultural roots of black people. The difference is that parents, teachers and others in authority over youngsters have become less judgmental, politically correct and lazy; therefore, speaking poorly is accepted.
Language is our tool of communication. If a person has poor oral language skills, he's likely to have poor writing, reading and comprehension skills. To my knowledge, there are no books in any field of study written in Ebonics or black English. It is very likely that a person with poor language skills will suffer significant deficits in other areas of academic competence such as mathematics and the sciences. It doesn't mean that the person is unintelligent; it means that he doesn't have all the tools of intelligence. That is what's so insidious about the state of black education today; so many blacks do not have a chance to develop the tools of intelligence. Many might have high native intelligence but come off sounding like a moron.
Black Americans should thank God that non-judgmental, politically correct people weren't around during the early civil rights movement when blacks began breaking discriminatory barriers. Discriminatory employers would have had ready-made excuses not to hire a black as a trolley car motorman, cashier or department store sales clerk.
There are some significant challenges to being judgmental and politically incorrect and insisting on proper language. A professor or teacher can get cursed out by students or parents. A black student who speaks well, carries books and studies can be accused of "acting white" and find himself shunned and assaulted by other students.
I would be interested in hearing the teaching establishment's defense of permitting poor language.