Since notorious street gang MS-13 put down roots in the D.C. area, officials in tiny Arlington County have worked to establish one of the most extensive gang prevention programs in the region, focusing on keeping children out of gangs and helping current gang members get out.

Arlington documented 10 active street gangs in 2011, and 237 gang members came into contact with police in the same year. But the county has more prevention programs than any of the surrounding jurisdictions. And officials say its efforts are part of the reason Northern Virginia has seen a 34 percent decrease in gang activity since 2003.