The least educated American workers, who took the hardest hit in the Great Recession, were also among the slowest to harvest the gains of the recovery. Now they are a striking symbol of a strong economy.

The unemployment rate for those without a high school diploma fell to 5.1 percent in July, the Labor Department reported Friday, the lowest since the government began collecting data on such workers in 1992. At the economy’s nadir in the summer of 2009, the unemployment rate for high school dropouts hit 15.6 percent, more than three times the peak unemployment rate for college graduates.

Buffeted by technological change and seemingly out of place in an economy where skills and credentials are in ever more demand, this cohort struggled while more educated workers scored jobs and promotions and rose on the economic ladder.

High school dropouts make up 7.2 percent of the labor force, and some experts doubted they and other low-skilled workers would ever fully recover from the effects of the recession, said Betsey Stevenson, a professor of economics at the University of Michigan.