BigReveal is an iPad app that lets you create personalized scratch cards. You use the app to hide a picture under a silver coating, just like a scratch-off lottery ticket.
This app can be highly motivating to students. For teacher and staff, it can help evaluate how well students can swipe up, down, right or left and if they can access all areas of the screen, which can be helpful when trying out a new stylus or mouse.
This app is not free, but only cost $1.99. It might be a good investment for use with your students.