Originally Posted by article
An alternative approach—skill-based sorting with a uniform curriculum—involves just one of the two components that define tracking: sorting by skill, while not differentiating the curriculum based on students’ skills.
Apply this to what is termed "1st grade", with some kids coming in with a skill set indicating "6th grade" level and it is quickly seen that what they describe would not serve those children well. Despite grouping children with similar incoming skill set together, if all students receive the same curriculum, groups of students coming in with a "1st grade" skill set may be expected to gain one year of knowledge after a year, while the groups of students coming in with a "6th grade" skill set have not moved ahead, may have stagnated, or possibly regressed after a year.

I did not find a portion of the article which considered grouping by readiness and ability regardless of age, to keep ALL students learning, acquiring knowledge, and moving forward. This is conspicuous in its absence.

Originally Posted by article
The new Common Core State Standards also attempt to strengthen academic curriculum across
the board, reducing the differences in students’ curriculums.
In concert with the first excerpt quoted above, this second excerpt does not seem to present an understanding of Common Core as providing a "floor, not a ceiling." Might the University of Chicago Consortium on Chicago School Research and its "thought partners" have this wrong?