tl;dr:<p>(1) Unlock exclusive content based on reading progress<p>(2) Include integrated discussion forums for each book where kids can discuss the content and their experience<p>(3) Include tests and quizzes about the content (and win prizes)<p>(4) Enable kids to earn the ability to publish their own work<p>(5) Include “hackable” books where kids of all ages can mash up the story and content<p>(6) Easily enable parents to incentivize kids with real-world rewards<p>All of these seem reasonable (which is not to say I necessarily endorse them). I am skeptical of #2 however. I believe it is good for kids to discuss what they read, but I think if I were a parent, depending on the age of the child, I'd be concerned about who my child is interacting with in the forums, and I could see it becoming a distraction from actually reading books.