A dispute has erupted over the results of a new study that shows that Minneapolis had the lowest high school graduation rate among 50 major cities.

The study, released by a Washington-based education group, showed less than 50 percent of Minneapolis students graduate within four years, and just 4 percent of all high school students in the city took the ACT or SAT college entrance exams.

Minnesota education officials are raising questions about the methodology and the data used by the Center on Reinventing Public Education, which advocates for charter schools and opposes teacher tenure rules. State officials say the participation on college entrance exams, for instance, is much higher than the group is reporting.

"It does seem that there are some serious questions about the way the data was analyzed, and if it was accurate," said Josh Collins, the Minnesota Department of Education spokesman. "It's unclear to me if there are meaningful conclusions that could be drawn from it."

The study came out as Minneapolis school leaders face mounting pressure to improve student achievement, particularly among students of color. Minneapolis officials have long known that many students have struggled, but the study was the first recent effort to draw a comparison to schools in other major cities.

Researchers with CRPE say they used data that included all the cities and that was publicly available. They said there is "no one perfect system."

The intent of the study was not to dwell on individual numbers, researchers said, but to highlight schools in top-performing cities and allow other state and local school officials to find out what the successful districts are doing right.

"We want people to see the holistic view of their city," said Jose Hernandez, one of the researchers. "Obviously there are lows and highs, but we want them to look at their cities as a whole and weigh them against each other."

The group also analyzed gains in math and reading proficiency, the number of students enrolled in advanced placement classes and other achievement measures.

Schools in Fort Wayne, Ind., graduated 90 percent of their students in four years. In Newark, N.J.; Philadelphia; Memphis, and Albuquerque, N.M., black students took advanced math classes at higher rates than white students.

Minneapolis ranked third in math proficiency gains, but was ranked low for reading gains.

CRPE used federal data to calculate graduation rates for all of the city's schools for the class of 2013. That includes charter schools plus all Minneapolis Public Schools' traditional high schools, contract alternative programs and schools with special programing, like special education.

The graduation rates used by the group were similar to numbers kept by the state's education department. In 2013, Minneapolis Public Schools had a 54 percent four-year graduation rate, but when the city's charter schools are included, the graduation rate in the city drops to 49 percent. Last year, the city's overall graduation rate increased slightly to 50 percent, with the Minneapolis district at 59 percent.

But the organization's numbers for students taking college-placement tests were far lower than the state's estimates. CRPE used self-reported data kept by the Office of Civil Rights.

A Star Tribune review shows some errors in the data used for the analysis. For instance, Minnesota Transitions Charter School is mistakenly counted five times in the study. If the data is corrected, the participation on college-entrance exams goes up to 11.5 percent, with Minneapolis Public Schools' participation at 12 percent.

Hernandez said they will correct the data and recalculate the numbers for the city.

In addition to the unreliable data, state officials question the organization's decision to compare the number of students taking the exam with a school's entire population, instead of just juniors and seniors, who are most likely to be taking college entrance tests.

Eric Vandenberk, a data scientist for the Minneapolis School District, said 72 percent of the district's 2012 senior class took the ACT.

"ACT completion rates have been a priority for several years," Vandenberk said. "Claiming a value of 4 percent is highly inaccurate and irresponsible and is completely not fair."

Daniel Sellers, executive director of MinnCAN, a group pushing for education changes, said state education leaders should not disregard how Minneapolis compares to other cities.

"We often see state and district leaders who are complacent about a very slow pace of change or no pace of change," Sellers said. "Hopefully this report, which compares us to our peers across the country, shows us that it can be better and needs to be better."

Alejandra Matos • 612-673-4028