iTunes U is a rich resource of knowledge available to you right through your iPhone or iPad. Recently, users of the app may have noticed that some iTunes U courses now offer closed captioning. In order to view the closed captions in the app, however, you need to enable them. Many users assume that the closed caption settings are under iOS's general Accessibility settings, but they're actually found in the settings of the iTunes U app itself.
As iMore points out, users with disabilities simply need to navigate to iOS's Settings app, then select iTunes U, and then toggle Closed Captioning to "On." Closed captioning isn't just helpful for those with disabilities, either. I have a friend who hates wearing headphones, but likes to view iTunes U materials on his train ride home. He simply enables closed captioning, and he's able to follow his courses sans headphones and without annoying his surrounding passengers.