Watch Doc is a great Chrome Extension that I only discovered this summer. Once installed in your Chrome Browser, it will notify you when any of the shared files in your Google Drive have been updated. I have many docs that once shared live somewhere in the depths of my Drive never to be seen again. This way I am visually prompted whenever someone adds something new, or better yet, when a student is adding to their work that they have share with me. Click on the picture below to get started.