One of my biggest struggles with Google Classroom was keeping up with late work. Actually that is a struggle all the time regardless of Google Classroom. My solution to keep on top of grading late work is to have students complete this Google Form to let me know they turned in late work. I know I can check the spreadsheet of these form responses for new late work, grade it, update it in my gradebook, then mark on this spreadsheet that it was done. I would tell my students your late work doesn’t exist without this form. It is the only way I will know to go find it and grade it.