>the US, with its uniquely devolved set of educational authorities and standards is alone in the developed world in terms of the inequality of education offered to its children.

In terms of primary and secondary education, absolutely. In higher education, inequality is common across countries, but higher education has a much smaller average effect on actual life outcomes than childhood education. Yet somehow reforming the school system (and the avaricious correlation between property taxes and outcomes) gets a lot less political oxygen.

I assume you either have little experience with the US school system or other countries school systems.

There is most definitely similar inequality in other countries.

Do they also have a permanent underclass with a high crime rate and result in mass incarceration?

Permanent underclass? Yes.

Mass incarceration? Depending on your definition

Every other country has a similar system. Even the Soviet communists, at the height of their power, had more or less the same system.