A few of the Sudanese refugees have achieved striking success, becoming teachers and engineers and pursuing graduate degrees. But many others have resigned themselves to low-wage work like parking cars or mopping school floors. A few have run afoul of the law. Their numbers in the area, roughly 150 at first, have dwindled by perhaps half, as men have migrated to other states for work or returned to South Sudan.

Jacob, who was elected head boy of his high school in the Kakuma camp, was considered a leader among the refugees. Eight years after arriving in the United States, he moved out of Clarkston and into a small house he built with Habitat for Humanity in a tidy low-income neighborhood in southeast Atlanta. As he entered the academy, he was completing a term as chairman of the Georgia chapter of the Sudanese People’s Liberation Movement, the political party that has governed South Sudan since its independence from Sudan in 2011. If he had a grand dream, it was to use his police career as a springboard to law school, so he might go back to a homeland he barely knew and teach his countrymen the ways of American justice.

On Sunday afternoons, Jacob gathered with other South Sudanese immigrants at St. Michael and All Angels Episcopal Church for a service that fluctuated between English and Dinka, often in the same sentence. As drummers beat out a welcome, Jacob joined the men in shiny suits and buffed shoes who occupied the pews on the left. Their statuesque wives, swathed in boldly colored head wraps, split off to the right along with the children, some of whom slouched in tight jeans, N.B.A. jerseys and Spider-Man T-shirts.

Immigrant backgrounds are not unusual among police recruits in Atlanta. But few in Jacob’s class were as new to the country, and certainly none had been reared in a mud hut or paid a matrimonial dowry that included 30 cattle. His South Sudanese friends worried that his heavy accent and ebony skin might make him vulnerable and wondered whether he had the swagger to be an American cop. His own mother, Mary Ayen Kur, who lives in Kenya, said he had stood out among her seven children for his turn-the-cheek gentleness. During a visit to Atlanta, she told me: “He was born like a pastor.”

Jacob’s first term at the academy was short-lived, as he pulled up lame during a fitness test on Day 6 with what was later diagnosed as a stress fracture. Such setbacks are not unusual; three of 10 recruits do not make it through on their first try, either because they are injured or fail the tests of firearms skill, emergency driving or physical fitness. After recuperating for four months — while answering phones for the fugitive squad — Jacob joined a new class last January. He showed up both confident and anxious on the first day of the 22-week course for a crack-of-dawn session euphemistically described as orientation. For two hours, the academy instructors demanded push-ups, jumping jacks, stress positions and bear crawls, often with weighted duffels held overhead. Paramedics were positioned nearby to haul away the wounded.

“Get that bag up, Mach!” one sergeant hollered. “Solve the problem, son.”

“You look like a bunch of future Best Buy employees,” Officer Hardy Carrow said with a smirk.

Jacob’s face showed equal parts exhaustion, humiliation and fury. But as sometimes happened at such moments, his thoughts drifted back to Africa, to the two-month walk from Sudan to Ethiopia. “That was worse,” he told himself. “There is nothing more difficult than what I have gone through. They’re only trying to see whether you quit, whether you’re strong, whether you can deal with the stresses.” His ability to adapt to a hostile environment was one thing he liked best about himself.