Assimilation only works where there is a majority white school system and the blacks have to fit into the white norms. How many blacks do you need for them to gang up and start acting the way they do in this essay? Probably not too many.
There is also a moral question: even a small number of blacks in a school who are there to "assimiliate" are there to take (socialization) from whites, and presumably slowing down the rate that whites would learn at if they weren't paying a "tax" in accomodating blacks.
Is it really moral to give some kids a lesser education so that others (the less teachable) get a better one? The black kids are getting extra resources, the whites extra burdens. At some point this becomes manifestly unfair.
I've encountered EXCELLENT all-black classrooms and programs. Again, the problems start emerging when the students aren't held to the strictest standards of behavior and accomplishment, no excuses, no warnings, no second chances.