When my students do their math homework and struggle with a problem, they often wait until the next day to ask me about it. Occasionally they will email me with a jumbled message in an attempt to type algebra. While these are not terrible options, Google Drive provides an even better (and faster) way for students to get help with a problem. Now that my students are doing their homework on their iPads, this process is even easier!
When a student has a question about his work, he can take a screenshot on his iPad of his attempt at the problem in Notabililty, save the image to his Google Drive, and share the image with me (and preferably add a message asking a question about the problem).
When I get an email notification that a student has shared an image with me, I can give him feedback quickly by opening the image in Google Drive and inserting text comments on different portions of the image. He will see these comments immediately.