A chart comparing district and charter schools' principal turnover rates, from today's "State of the Sector" report.

A sweeping look at who attends charter schools in New York City, and how they fare, shows that the sector excels at advancing academic achievement but struggles to enroll high-needs students and to retain staff.

For the past nine months the New York City Charter School Center and a team of charter school founders have collected and crunched data on 35 different topics, including test scores, demographics, attrition, and enrollment. Their findings are laid out in a much-anticipated — and much-delayed — 40-page “State of the Sector” report, released today.

The report represents an inaugural effort to be more transparent about how charter schools in New York City are doing. Coming from a group that more often celebrates charter schools’ achievements, the report offers a blunt self-assessment of the sector, illuminating its shortcomings in student enrollment and staff retention while at the same making a case for it to continue to expand.

For instance, the report acknowledges “striking” staff attrition trends — nearly one-third of city charter school teachers leave annually — but points out the sector’s ability to achieve high academic results anyway. And while the schools serve low rates of students with special education and English language learners, the report emphasizes that those who do enroll tend to do better than their counterparts in district schools.

The report was originally scheduled to be released nearly two months ago. But the center needed more time to verify the data, then held the report until it could be released along with “dashboards” showing individual schools’ statistics, according to CEO James Merriman. Those dashboards were published on the center’s website today, although they have withheld  some data, including staff attrition. 

The findings confirm and herald high test scores, attendance rates, and parent satisfaction at the city’s charter schools, which serve about 47,000 New York City students and are growing.

But they also confirm critiques that have been heaved at the sector, including charges that charter schools don’t always serve the neediest students. Charter schools lag behind significantly behind district schools in serving English language learners and slightly behind when it comes to students with disabilities. And while the vast majority of charter school students are eligible for free or reduced-price lunch, 80 percent of charter schools have fewer poor students than their district average.

Perhaps more startling are the figures about how many teachers and principals leave charter schools each year. According to the report, a third of charter school teachers leave their schools each year, compared to about 15 percent in district schools. And charter school principals leave six times as frequently as district principals – more than 18 percent each year, compared to less than 4 percent in district schools.

And the findings also reveal several points of tension within the charter school sector. For example, the report says that “NYC charter school leaders have mixed opinions about backfill enrollment” — whether schools should accept new students to replace those who leave over time. District schools are obligated to enroll new students to fill vacant seats, but charter schools can choose to forgo state funding and leave the seats open instead.

Some charter school advocates think that backfilling seats is essential to the sector’s mission of serving at-risk students. But others argue that charter schools cannot be expected to fulfill a mandate of moving students forward if they continually accept students who would not be on par with their classmates. The report acknowledges that charter schools’ performance probably benefits from the flexibility, especially if it is low performers who leave most often. Charter middle schools, which backfill seats least often, post the strongest performance.

Dick Riley, a spokesman for the United Federation of Teachers, said the report fell short because it did not sufficiently contend with the backfill issue. ”The report fails to quantify just what the impact is on test scores when students leave charter schools and are not replaced,” he said.

People involved in creating the report said the goal wasn’t to promote just good things happening in charter schools or to prescribe solutions, but to present data that could illuminate areas where solutions might be needed.

“The only way that the charter school community is going to get better and earn the right to serve more students is to be transparent about our results, both the strengths and the gaps, and to be relentlessly committed to continuous improvement,” said Dacia Toll, co-CEO and president of Achievement First, a network of charter schools in Brooklyn.

But more information is needed to draw some conclusions about the strength of the charter sector, the report cautions. The sector doesn’t have good information about why teachers leave or where they go, so it can’t conclude whether high teacher attrition is a problem. Similarly, data about student mobility in both charter and district schools are thin, making it impossible to understand the impact of student attrition on performance, the report warns. And the report suggests two possible reasons for lower special education enrollment — lower identification rates and poor perception from parents of children with disabilities — but says more research would be needed to conclude what impact those phenomena might be having.

Merriman said he expected that the data — and the holes in the data — would leave the sector vulnerable to criticism from its regular critics. But he said hoped the new transparency would ultimately lead to more a productive policy conversation about where charter schools fit into the New York City school system.

“Any time you try to have a rational conversation around data there will be people bent on misusing the data and there’s little that anyone can do around that,” Merriman said. “My hope is, as the report says and I believe we’re justified in hoping this, that this will lead to a more thoughtful, balanced and data-driven conversation.”

The full “State of the Sector” report is below.