Speak screen doesn't work 'really well' for iBooks.
Go to Settings-> General -> Home Header -> Select the option: 'VoiceOver'.
Then go to the iBooks app and open an ebook from your library. Press the Home button three times to activate VoiceOver. Then tap the first sentence once and drag down with two fingers to start reading. Reading continues until you tap the screen with two fingers. Press the Home button three times to turn VoiceOver off again.
While reading, you will notice that the VoiceOver reads in a very hurried manner. You can optionally adjust the speed using: Settings -> General -> Accessibility -> Activate the option: 'VoiceOver'
The VoiceOver in combination with iBooks is fun to try out, but does it really read aloud? No…