The system does not automatically put the score (score out of:) on each discussion post, when you have checked "assess each message and automatically calculate the topic score." This option should only be checked, if you want to manually input a score for every post made to a particular topic. If you check, "assess each message and automatically calculate the topic score," the system will perform the Calculation specified in the dropdown. For example, if a student posted four times to this particular Discussion Topic, you've selected this option with "average" as the Calculation choice, you've already manually input a score for each of the four posts, then the four scores would be averaged to produce one score in the gradebook.
You may want to see FAQ # , which explains how to list all the posts by a student for a particular topic, and place one score in the Grades area for that Topic.