Arne Duncan, a managing partner of the Emerson Collective, was U.S. Education secretary from 2009 to 2015.

The latest results from the National Assessment of Educational Progress (NAEP) are prompting some soul-searching about the limited gains over the past decade, but there are outliers worth saluting. More important, we should be analyzing what successful states and school districts are doing differently so that others can learn from them.

Let’s start with the District. Scores in the city increased by three points apiece in fourth-grade math, eighth-grade math and eighth-grade reading. In fact, among the 50 states plus the District, D.C. was the only one to post an increase in eighth-grade reading.

Another bright spot is Mississippi, which has the highest poverty rate in the country and is in the bottom five states for per-pupil education funding. This year, the state ranks No. 1 in the nation for gains.

Mississippi was the only state with an increase in fourth-grade reading, posted the largest gains in fourth-grade math and was one of only three states with an increase in eighth-grade math. Mississippi has put a big focus on literacy, high standards, tests that are well aligned to the curriculum and a strong accountability system. It has also invested heavily in teacher training.

Louisiana posted nation-leading gains in eighth-grade math while Nevada is up four points in fourth-grade math. A decade ago, Tennessee ranked near the bottom in the country. Today, on all four tests, Tennessee is at or near the national average thanks to a strong commitment to high standards, quality curriculum and robust accountability.

At the district level, Denver gained six points in fourth-grade math and four points in eighth-grade math. Cleveland is up three points in fourth-grade math.

These states and districts share a couple of characteristics. Most have had bold, consistent leadership for several years. Carey Wright has been Mississippi’s education superintendent since 2013. John White has been Louisiana’s superintendent since 2012.

The eight years of leadership in Tennessee under Gov. Bill Haslam (R) ensured that reform strategies led by state chiefs Kevin Huffman and Candice McQueen received adequate time and support to succeed.

At the district level, Denver’s Susana Cordova has seamlessly built on the progress of Tom Boasberg , who over a decade built a diverse, high-quality portfolio of schools that have made his one of the few large urban districts gaining students. In the District, even with some turnover at the top, the city has charted a steady and purposeful course; for more than a decade, leadership has made a big bet on teacher quality and expanding school choice.

All these districts have been serious about building capacity to support teachers. They have ambitious strategies around talent development, as well as high standards and high-quality curriculum. They share a deep commitment to transparency by keeping parents, principals and teachers fully informed about where they succeed and where they struggle.

They have had the courage to do things that are politically difficult and unpopular, such as evaluating teachers and implementing robust accountability systems. They didn’t succumb to anti-testing fever but instead worked to improve assessments so they required less testing time and more timely feedback for students, parents and educators.

They invested smartly in the things that students need: quality early learning, more learning time, high-quality curriculum, community schools, wraparound services and well-trained, well-supported teachers.

These successful school leaders take time to learn from each other and share best practices. They understand that improving schools and school systems isn’t rocket science, but change only happens if it is implemented with courage, consistency and commitment.

Still, the NAEP results are sobering. We should be seeing more progress.

The one thing the United States cannot do is use these results as an excuse to go backward to the days when standards and expectations were low. We cannot return to a time when achievement gaps around race and poverty were hidden. We cannot pretend that talent strategies will happen on their own without intentional efforts to recruit, support, retain and hold accountable educators.

Above all, we can’t stand still. Today, a greater share of our public-school students live in poverty , and they are more diverse than ever. They face economic and social challenges earlier generations never faced. In this economy, education has never been more important to our collective success, and the urgency to improve has never been greater.

The proof of what is possible is all around us. The time for excuses is long past. Our children are capable of anything if we just believe in them and invest in them.

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