After the latest Blackboard upgrade in December 2016, a new (old) feature has been re-introduced to your course sites: arrow buttons for navigating threads on the Discussion Board.
You’ll find these buttons in the top right corner of each thread page. If you use individual threads for each student in your weekly discussions, you might find these buttons particularly helpful for navigating from thread to thread, or to jump to the first / last thread with one easy click.
Happy navigating!