You can download a spreadsheet (xls) of grades for an entire classroom. In the Teacher Control Center, click "Monitor" from the top navigation menu. Your active classrooms are listed in a grid view, with the name of the classroom and their activities displayed. Click the button to the right of the classroom name to download the spreadsheet.
The workbook will contain a sheet (tab) for each activity, and each sheet will have grades, time on task, and data about each student's best design listed.
Note that the spreadsheet is generated on-demand and is a snapshot of what your students have completed at that time.