Audiologists (hearing specialists) can determine if a child has APD. Although speech-language pathologists can get an idea by interacting with the child, only audiologists can perform auditory processing testing and determine if there really is a problem.
Some of the skills a child needs to be evaluated for auditory processing disorder don't develop until age 7 or 8. Younger children' brains just haven't matured enough to accept and process a lot of information. So, many children diagnosed with APD can develop better skills with time.
Once diagnosed, children with APD usually work with a speech therapist. The audiologist will also recommend that they return for yearly follow-up evaluations.