Overview
A discussion assessment allows learners to earn points by participating in a single thread of discussion that is started by the instructor. The description of the assessment is essentially the first 'posting' to the thread, and the learners can then reply to the posting and subsequent replies. At the end of the assessment, the instructor grades each learner based on their postings.

The 'Discussion' section of the assessment is where the initial posting from the instructor is displayed and where learners can respond to any posting in the discussion. Instructors and learners can subscribe to a discussion assessment, by visiting the Discussion tab, then click 'Subscribe'.
You can enable an option that requires learners to post before seeing the discussion. This prevents learners from viewing the thread first and copying someone else's response. To enable this option, go to the assessment click edit and check the checkbox under Options.

Also here, you can enable an option that lists most recent posts first.

Submissions
Learners can see the discussion thread by visiting the Discussion tab. They can then reply to any part of the thread by clicking 'Reply', entering their comment, then click Save. A student will see all of their postings highlighted with a "crown" icon.
Learners can see how many times they've posted to a discussion by looking at the 'Your submission' area. A list of all their responses is displayed together with links back to the discussion on the overview page.

Grading
The 'To grade' tab lists the number of posts each learner has made to the discussion.
If a learner has posted at least once, you can see their posts and enter their grade by clicking on their

icon.
You will see the full thread for each thread that the learner participated in and the learner's postings will be indicated with a crown icon.