Wizard of Oz – Hidden Difference combines puzzle solving, audio narration and illustration in one educational iPad app.

The 69p app from SecretBuilders features more than 50 levels, which are full of puzzles to help develop visual and spatial problem solving skills in children aged three to 13. Each level, when conquered, unveils a scene featuring audio and illustration from Oxford University Press’ Bookworms Series edition of the Wizard of Oz.

There is also a free version of the app that features a handful of levels.