In the 18 years since the fight and its fallout, that sentiment has evolved as Mr. Carson, 35, has turned around his life. He took up work as an activist, minister and mentor to young people going through the same challenges he faced. Then this year, he added an improbable line to his résumé: Decatur school board member.

Yes, Mr. Carson won election to the very board that expelled him.

To many here, Decatur has largely transcended its past racial rifts. Residents talk proudly of Decatur as a place where people do not bat an eye when they see a mixed-race couple and where millions of dollars have been pumped into efforts to help marginalized children.

Still, this is a place where black people make up about a quarter of the population, but have accounted for 42 percent of police traffic stops since 2010. At nearly 24 percent unemployment, black Decaturans are two and a half times more likely to be unemployed than white residents. And some black residents remain on the civic fringe, avoiding downtown or community festivals that they say do not cater to their culture.

Mr. Carson operates in that tenuous spot between hope and unrest.

He applauded Decatur as a place where “we really have that hard conversation” about race, where the white police chief has been serious about investigating allegations of racism in his department.

Yet he ran for school board in large part because racial disparities remain among students. Even after he turned his life around, he encountered problems all too familiar to many black people here and around the country, from difficulty getting a job to uncomfortable encounters with the police.