They are automatically promoted and eventually graduated out of high school, primarily because the school system does not want to deal with them anymore. Someone else's problem now.
They are admitted into college on affirmative action. They get to major in two marshmallow fields "recreation and sports" or "elementary education". Even in those easy fields they get a free pass. The college doesn't care, they got their tuition.
Next stop, government job. How 'bout teaching?
You’re right; the bar has consistently been lowered for them, to the point where no private employer has any use for the resulting semi-literates. Uncle Sam steps in with fake work, and we pretend assimilation has worked. I’ve posted on other threads that without gubmint jobs black unemployment must be near 95%.
FWIW, there is a measure of job security in this for Anglos; employers (outside of the government sphere) need people actually capable of working.