> the only seemingly rational explanation for inequity is discrimination

Wait, this is not what I said and is not how serious social science is done. In many ways, public K-12 education is equally abysmal for everyone. It may not overtly discriminate, but it lets people fall through the cracks in a way that amplifies the causal influence of pure luck (i.e. randomness, noise in outcomes) and external factors such as different cultural attitudes and generational history (such as whether your grandparents and great-grandparents happened to be educated or at least literate), that account for much of the observed correlation with race.