https://help.blackboard.com/Learn/Instructor/Ultra/Grade/Grading_Tasks/Work_Offline_With_Grade_Data
How to Download Grades From the Grade Center
You can download full or partial data from the Grade Center. Once downloaded, grades and comments accessed through the Quick Comment feature or Manual Override page can be changed and added offline and later uploaded to the Grade Center.
1. Click into your course and then click the Gradebook tab.
2. Click the link to download the gradebook:
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3. Choose the appropriate options such as Full Gradebook or Grade History. Select everything you want to download. Select the file delimiter, Comma or Tab.
4. Click Download.