Doing collaborative work in Google is simple and very efficient. Say you are working with colleagues building PBL units or common planning documents and someone remembers they deleted a big section two days ago that they really wish was still there. Or, you are just monitoring Documents/Slides/Sheets being built collaboratively between students and one student says they have been adding content but somehow it is magically disappearing. Besides, it is great to know who is doing what work. What do you do? You use Revision History to see the living history of that item. This great video below will walk you through how it works and advanced options.