CARROLLTON, Ga.—Breonna Daniel, a onetime high-school dropout, was smoking pot and "hanging out with the wrong crowd" last year without a hint of concern for her future.

This summer, she is among hundreds of teens working on Southwire Co.'s factory line four hours a day, earning above minimum wage and spending eight hours a day in the company's classrooms. It is part of a novel program designed by the cable manufacturer to develop a skilled workforce and get troubled high-school students from the community back on track.

"I didn't really care about school or the situation I was in," says Ms. Daniel, 17 years old. The program "changed me. I've grown up."

The initiative by Southwire, a closely held company with 7,500 workers, is among the latest attempts by U.S. companies to produce what the education system too often struggles to deliver: high-school graduates with adequate workplace skills. Companies across the U.S. say that without better educated workers they will lose their competitive edge in the global economy.

The U.S. high-school graduation rate hit 81% in 2012, according to the latest data available from the Education Department. That's up from 74% in 2007, an improvement largely attributed to a reduction in teen crime and pregnancies. But American high-school students still lag behind their peers around the world in graduation rates, ranking 22nd out of 28 developed countries tracked by the Organization for Economic Cooperation and Development.