A report we released last week painting a picture of urban education across the nation has caused a stir in Minneapolis ("School study's results disputed," Oct. 9). We'd like to set the record straight.

Our report, "Measuring Up," looked across district and charter sectors and beyond test scores to learn about educational achievement and opportunity in 50 cities. While there were bright spots, no city performed at the top on all of our nine indicators of performance and equity, and every city showed areas that need urgent improvement.

In Minneapolis, there were very challenging findings as well as bright spots. Our research showed recent overall achievement gains for students attending Minneapolis district and charter schools. But the city looked comparably weaker on graduation rates and enrollment of low-income students and students of color in top-scoring schools.

Our study relied on publicly available data, in large part so that anyone could reproduce the findings. For three of our indicators, we relied on a federal data set from the Office of Civil Rights (OCR). This is where the firestorm comes in.

Understandably concerned by these poor outcomes, especially regarding the low ACT/SAT test-taking rates, officials from the Minneapolis Public Schools and a Star Tribune reporter looked into the data and brought an inconsistency to our attention. One Minneapolis charter network had inaccurate information in the OCR data, miscounting the total number of students within the network as the total number of students in each of the network's individual schools.

Our researchers could not have known in advance about the error in the federal database, but were happy to work with MPS to correct it immediately. Since we had no way of confirming what the accurate data should be for that charter network, we removed the five schools from the analyses and revised our figures for Minneapolis accordingly.

After we made these adjustments, three sets of results for Minneapolis improved: the ACT/SAT test-taking rates for 2011-12 increased by 8 percentage points, from 4 percent to 12 percent. The citywide out-of-school suspension rates for 2011-12 went from 10 percent to 7 percent. And the rate of all high school students taking advanced mathematics courses in 2011-12 increased from 5 percent to 16 percent.

MPS and others have raised other issues about how we calculated ACT rates and graduation rates. We stand by those methodologies as the best possible way to make comparisons across cities, given available data.

Rather than ask what can be done to improve Minneapolis' results, some have instead chosen to attack the Center on Reinventing Public Education's credibility and have questioned our motivation for publishing the study. The center has been accused of being pro-charter, anti-teacher-tenure and in the pocket of big corporations. Readers who review our report will have trouble seeing any such biases. They will see instead that we say results from the 50 cities suggest that there is no single form of public school, not charter nor traditional public, that meets all of the needs of all urban students.

Some have also accused us of secretiveness, but readers can see that we relied on publicly available data and shared all of our methods so others can check or reproduce them. As with all of our reports, this one was independently peer-reviewed for rigor and balance.

Other cities are taking a hard look at our data, analyzing the reasons for troublesome results and trying to learn from other cities that have made greater progress. This is exactly what we had hoped for. We wanted our report to help civic and education leaders to see how all of their public schools are doing and to benchmark against other cities, particularly those with similar demographics. The goal was to get beyond comparisons between district and charter schools to spark conversation and shared strategies for tackling the thorniest challenges.

We're disappointed that the conversation in Minneapolis has been derailed by a data irregularity, which, when brought to our attention, we addressed immediately. We're even more concerned that some are choosing to attack the messenger instead of taking an honest look at how well the city's schools are serving all students. When the furor over our report dies down, we hope those who care about Minneapolis' students will redirect their conversations to what matters most — improving outcomes and opportunities for all kids.

Robin Lake is director of the Center on Reinventing Public Education, affiliated with the University of Washington Bothell.