https://itunes.apple.com/au/app/notability/id360593530?mt=8
Notability is priced at $2.99, it has great features but the one that particularly inticed me was the ability to record audio. If you were to use this app in the classroom I particularly like the fact that audio can be recorded as well as text, pictures etc.
The web site with hints and tips can be accessed here.
I have added a tutorial by newingtonict (you tube) below