AdvancED is a private accrediting firm working with more than thirty thousand schools worldwide. A team from its Southern Association of Colleges and Schools division arrives in Birmingham today. They're checking whether Birmingham City Schools are fixing problems that led the agency to put the system on accreditation probation last summer. It got WBHM's education reporter Dan Carsen thinking about what these firms actually do, and whether they have as much power as it seems. He caught up with AdvancED president Mark Elgart and asked him how his agencies decide which districts get accredited ... and which don't.