I do not find the excerpt you provided, in the article posted above. Possibly it is in a different article?
The article you posted
https://www.educationnext.org/what-...-americas-most-challenging-high-schools/"Occasionally principals would tell me they didn’t need AP, IB or Cambridge. They said they could make their own courses just as demanding. I determined that rarely happened because their homemade final exams were not written or graded by independent experts outside the school, as AP, IB and Cambridge exams were. If classroom teachers controlled the tests, they tended to be gentle with those nice students they knew. That ruined the principals’ hopes for tough grading and high standards."
No evidence to support.
(I have also had many conversations with him)
