He zeroed in on high expectations as one of the factors in the school's success in boosting test scores and attendance.
Other keys were leadership, a hard-working staff, honest conversations about data and community involvement, Duncan said. "There wasn't one simple answer here," he said, "and there never is."
In an hourlong roundtable with teachers, administrators, parents and students, Duncan probed what it was like for Christian Folau, a former Northwest student, and Maria Moreno, president of the school's PTA, to experience the changes.
Folau, now at East High School, was an eighth-grader when the then-new principal, Brian Conley, began transforming the school in 2010.
"Teachers were demanding a lot from me in eighth grade," Folau said. "It was hard and I didn't like some processes, but it did help me …What was helpful was they sat down with me."
Moreno told how she first volunteered at Northwest after her son, transplanted from California mid-year with his family, was bullied and had a fight in the school bathroom.
Were the changes resisted? Embraced? Were they scary? Duncan asked Moreno.
"It was a better change," she said.
Another son now hates to miss school at Northwest, and worked hard to get into the Warrior Club for high grade-point average students, she said.
"We don't have kids fighting in the bathroom anymore," she said.
Duncan also asked what Northwest is doing to impart non-academic lessons such as grit and resilience, which research shows is important.
He is traveling around the country to learn what is and isn't working to improve schools. He came to Utah after telling Nevada educators that schools need to set higher expectations.
McKell Withers, superintendent of the Salt Lake City School District, said he bristles when legislators talk about "bottling" what works in any particular school.
"A district has to be smart enough to realize there isn't a silver bullet, a single answer, a program, a book or a curriculum… It's about investing in people."
Duncan said the federal money that kick-started Northwest's change a $2.3 million school improvement grant for the Title 1 school was less important than what administrators did with it.
"While resources help, what matters most is culture and high expectations and that's embodied in this school."
Tech, data, teacher pay
Read more here about the strategies Principal Brian Conley and educators at Northwest Middle School are using.
Do you know an innovative teacher?
KUED-Channel 7 and The Salt Lake Tribune are looking for nominations for upcoming Teacher Innovation Awards, recognizing educators who are using digital media to improve students' learning.
Teachers from across the state can be nominated in five categories: arts, math, reading and language arts, science and social studies. Learn more at kued.org/nominate.