This app allows teachers to create assignments with their students in real time by using an interactive drawing board! It also has other features that are useful such as creating quizzes, sharing files via Google Drive or DropBox etc., but this feature takes some getting used too because it's not intuitive at first sight like most of these sort apps out there nowadays (I'm looking forward though!).
I'd really recommend trying one before buying - if you're serious about your learning then try different ones until find what works best!! You can use any subject material from Maths through Chemistry up till Physics-related topics which makes its versatility amazing compared to many others around now days.