A Tulane University institute that studies changes in public education in New Orleans after Hurricane Katrina announced the resignation of its executive director Monday, weeks after retracting a study on the city’s public high schools.

John Ayers’ resignation as director of the http://www.coweninstitute.com/">Cowen Institute for Public Education Initiatives is effective Nov. 30. The reason for his departure wasn’t released.

On Oct. 1, the institute issued a study which it said indicated that the city’s public high schools appeared to be exceeding expectations for the education of students suffering various disadvantages. But the institute retracted the statement nine days later. Ayers issued a statement saying the methodology was flawed and the results, therefore, were inaccurate.

The resignation was announced in a statement issued by former Tulane President Scott Cowen, a founder of the institute.

“I want to thank John for his contributions to the Cowen Institute, including assembling a talented staff, guiding a strategic planning effort and communicating our city’s educational progress as an ambassador for the institute, K-12 education in New Orleans and Tulane University,” Cowen said.

He said the institute’s chief operating officer, Matt Bailey, will serve as interim executive director.

The institute was begun in 2007 to assess the effects of the post-Katrina school reform efforts, including the takeover of most New Orleans public schools by the state’s Recovery School District and the widespread use of independently run charter schools.

The high school study defined vulnerable students as those who are more than two years above grade-level age in ninth grade, who failed an eighth-grade assessment test, who qualify for free or reduced-price lunches or who are eligible for special education services.

The study used a method known as “regression analysis.” It calculated the percentage of vulnerable students at each high school and came up with a performance score a school would be expected to achieve.

The study found 60 percent of New Orleans public high schools exceeded passage rates on end-of-course exams. Half had higher-than-predicted ACT scores, and all were at or above their predicted four-year graduation rates.

Ayers’ October statement did not offer details about the flaw in the methodology.