The third iteration of ISM Stability Markers® comprised 18 variables, each of which, according to ISM’s internal reviews, correlated strongly with a private-independent school’s ability to sustain excellence over time. In the fourth iteration, no additions or subtractions have been made to the 18 third-iteration Stability Markers themselves. The new scoring structure does, however, better align with ISM’s Success Predictors™. Benchmarks, weighting, points of reference, and/or methods of calculation have been updated to conform to ISM’s current perspectives on each. And one of these updates can be considered major: the movement of two first-tier markers (No. 5 and No. 6) to the second tier, replaced in the first tier by two previously second-tier items.