On August 24, 2021, Core Knowledge released new language arts materials for sixth grade. Although most of the material relies on additional books, included in the set is a reader on ancient Rome and another on social justice. The works are in draft form; I don’t know when the final versions might be released.
I’ll note as an aside that, in my view, the reading by Ida Tarbell on Standard Oil (in the work on social justice) is basically wrong. For a corrective, see Alex Epstein’s history.