The PBS app currently supports the latest iOS versions. For users with lower versions we regret to inform you that the app will not work on your device.
However, there is a workaround!
Open a browser window on your device and type http://www.pbs.org/ in the address bar. Once you are on the PBS.org website you can do just about everything you can do with the app. You can sign in, create a Watchlist, view your TV schedule, and of course view many of the PBS shows you love.