“In three years for sure I’ll be making two to three times what I am making now,” she told me.

It’s hard to muster enthusiasm these days for the prospects of workers on all but the topmost rungs of the labor market. Wages of high school dropouts are lower than they were at the turn of the century in real terms. The same goes for workers with a high school diploma, and also for workers who went to college but stopped short of a bachelor’s degree.

This stagnation kindles the insurgent campaign of Donald Trump, who promises to somehow fix everything by walling off Mexico and slapping anti-dumping tariffs against China.

An overwhelming majority of economists have panned his “solution” as a distraction — indeed, a surefire way to cripple the economy. Still, the appeal of Mr. Trump’s message underscores the hopelessness of many workers and the helplessness among policy experts struggling to find a fix for a labor market in which it has become increasingly tough to make a living. As manufacturing’s share of jobs dropped to 10 percent from 25 percent over the last four decades, millions have been relegated to a low-paid service economy with no benefits, uncertain hours and little job security.

But are there really no ideas, short of throwing a wrench into the gears of the global economy? Ms. Edwards illustrates a surprisingly simple one: training for skills that are in demand. For some reason, this is a strategy the United States has not pursued earnestly in quite a long time. That looks like a mistake.

MDRC, the New York-based policy analysis group, last week released the preliminary assessment of an experiment called WorkAdvance, commissioned by the New York City government and funded in part by a federal grant. WorkAdvance offered targeted sectoral training programs for low-income workers in New York City, as well as in Tulsa, Okla., and northeast Ohio.