The city began giving annual progress reports to all of its public schools in the fall 2007. The reports give the greatest weight to how much progress students make from one year to the next on their annual state exams, in the elementary and middle schools.
High schools are judged according to progress students make in accumulating credits toward graduation, their state Regents exam scores and overall graduation rates.
Fifteen percent of a school’s grade is based on surveys of its environment completed by parents, students and teachers.
Last year, 25 percent of schools were given A's and 10 percent received D’s and F’s.
The city compares schools to a citywide average, and to a so-called peer group of schools with similar populations. For example, schools with many high-poverty students are compared to others in similar circumstances.
The IBO found this "reduces biased judgments due to demographics and sampling error between larger and smaller schools," according to its report (PDF).
Still, it warned that this doesn't mean all schools have an equal chance of getting high marks. Schools with a higher percentage of black and Hispanic students or special education students are slightly more likely to have lower progress report scores, the report said.
"For elementary schools, each 10 percentage point increase in the proportion of black and Hispanic students generally decreases the school's overall score by more than one point," the report concluded.
The maximum score a school can receive is 100.
For middle schools, each 10 percentage point increase in the proportion of black and Hispanic students generally decreases the school's overall score by more than two points. The correlation wasn't as large in high schools.
Raymond Domanico, the IBO's education analyst, said this could point to a flaw in the city's grading system. Or, he said, "Maybe the progress reports are fine but it suggests there's still a challenge in New York City of closing the racial gap of achievement."
Department of Education Spokesman Matthew Mittenthal acknowledged the correlation between a low score and a high concentration of black and Hispanic students.
"This is true, but it’s worth noting that this correlation was significantly weaker than it is on the state tests," he said, noting the IBO found no statistically significant correlation between students who are English Language Learners and the progress report scores even though these students tend to score lower on the state exams.
Mittenthal also said a grading system that looks at student progress is an improvement over one based solely on test scores.
An investigation by WNYC found high schools that earned A's and B's on their progress reports tend to take a small percentage of those special education students who require the most intensive services.