So Mr. King, a former Army commander who trained soldiers, founded Summit Academy, a vocational school. He spent years trying to persuade people to actually hire his graduates.
In 2009, as the nation was trying to climb out of the recession and Minnesota’s legislature was debating how to spend federal stimulus money, Mr. King sent busloads of his students to legislative hearings. They arrived early, filling out rows of seats normally occupied by lobbyists.
They showed up on construction sites in lab coats, carrying magnifying glasses, looking diligently for the black workers. They submitted a “missing-persons report” to local officials to highlight the lack of black workers on public projects.
The timing couldn’t have been better for Carmen Richardson. She had just quit her job plating metal for a pittance when she saw an ad for Summit. After she graduated from the program five months later, the biggest names in the construction business were competing for her.
“I was getting recruited like I was a basketball player,” Ms. Richardson said. “I was in shape, I was a female and I was black, so that was the golden ticket.”
She started out earning $24 an hour in 2011, and became a part of the carpenter’s union. She got a pension and full medical coverage. She bought a Suzuki motorcycle and, last year, a Dodge Charger.
“Got my first speeding ticket in that sucker,” Ms. Richardson said.
Now she earns $37 at Mortenson, a construction giant that played a critical role in opening doors for people like her.
“We knew that demographic shift was happening,” said David Mortenson, the company’s chairman. White Minnesotans, who sent generations of young men into the trades, were suddenly seeking a higher purpose — college degrees, office jobs.
Economic theory suggests that a strong labor market like Minnesota’s — and, increasingly, the country’s as a whole — makes outright discrimination expensive. Companies can hardly afford to turn away qualified people when there are so many jobs to fill.
Racial gaps do seem to narrow during better economic times. In mid-2010, just 67 percent of African-Americans ages 25 to 54 were employed. Among whites, the figure was 77 percent — a 10-point difference. Today, that chasm has shrunk to about six points, the smallest it has been since 2000.
Neel Kashkari, the president of the Federal Reserve Bank of Minneapolis, said that when he took the job two years ago, he was surprised that the bank’s economists couldn’t conclusively say what caused the divide.
“If we can’t even answer the ‘why,’ we can’t hope to design policy solutions to close those gaps,” Mr. Kashkari said.
Still, Mr. Kashkari said, companies do behave differently when workers are scarcer. That is certainly true in Minneapolis, where Mr. Mortenson helped force the city’s builders into action.
The company pushed trade unions to diversify their ranks and told its subcontractors “they weren’t going to get our business if they didn’t pull their weight,” Mr. Mortenson said.
It also hired diversity trainers to consult with almost every foreman and supervisor at all of its work sites, and brought in “cultural competency coaches” to work with high-level executives on implicit bias.