Using course tools>>Discussion Board>>Participating in forums
You can expand or collapse all the threads in a Discussion Board forum. You can also expand or collapse one thread at a time in a Discussion Board forum.
To expand or collapse all the threads in a Discussion Board forum:
Do one of the following:
Click Expand All on the far right above the messages to display all the messages related to all the threads.
Click Collapse All on the far right above the messages to hide all the messages related to all the threads.