Just for kicks I tried to figure out what Feinstein High School's rankings in RI-CAN's system would be in its last year before being named "persistently low-performing" and closed. In terms of overall performance FHS would have gotten a D with a score of 38%, although that's still ahead of seven other PPSD high schools. I'd note that the state average for high schools is a C-. The raw rankings by subgroup are pretty similar.
On the other hand, FHS easily would have been #1 in high school improvement this year, with a score of 13 points, easily besting Westerly's current top rating of 8.
All the achievement gap scores cannot be calculated, since there are not enough white or non-economically disadvantaged students for RIDE to release the numbers. Also, performance gains cannot be calculated for high schools.
So... this system seems to not be very informative or illuminating. The whole concept of in-school achievement gaps is useless for highly segregated school districts, like we have in Rhode Island.