The idea of eliminating the "D" is not new...Poland Regional High School in Maine opened with a version of this policy 10 years ago. The article captures part of the idea - disincentivizing work that isn't quite good enough to be called mediocre - but misses the larger idea that the elimination of the "D" at Poland and in other schools affiliated with the Coalition of Essential Schools was linked to: standards-based grading and assessment. What Mt. Olive has done may go part of the way - we'd need to know more about what it took to get a 63 vs. a 70.
We know from experience that raising standards works.