An objective states what a student is expected to demonstrate as a result of instruction or learning experience. Using the guidelines provided the Air Force ISD, learning is composed of three parts: knowledge, skills, and attitudes.
The objective has three parts. First is what the students will learn. The second is the condition under which learning will be performed, which includes the situations and the tools provided. The final part is the standard of performance which means the evaluation of what is considered acceptable performance.
In a discussion you want students to demonstrate the learning through speaking or writing. This means the instructional designer should review with the subject matter expert and identify the components of the learning. These can include key principles, perspectives, examples, connections, inferences, important skills, and attitude.
The condition will focus on the resources that they can use to demonstrate their knowledge. In a course this will be the textbook, suggested resources, and external resources chosen by students, which may include the source.
The third consideration of a discussion is to determine the acceptable level of performance. A major online university will usually provide this through a rubric which will consider multiple standards and the levels of performance that will be measured. For example one standard would be the quality of the content:
Excellent : demonstrates and applies in-depth, accurate knowledge of the material.
Good: demonstrates and applies accurate knowledge of the material
Unacceptable: demonstrates limited or inaccurate knowledge or inability to apply the material.
Here is an example of discussion prompt that has the three constituting parts of an objective:
Using the information provided in chapters 7 & 8 on emotional intelligence, give your own example that illustrates at least three of the author’s main concepts.
Air Force ISD: http://www.au.af.mil/au/awc/awcgate/edref/afman36-2234.pdf
Examples of Good Discussion Questions: http://www.uwosh.edu/d2lfaq/teaching-resources/discussions/discussion-question-tips-and-pointers
Example Discussion Prompt and Response: http://campustools.capella.edu/BBCourse_Production/PhD_Colloquia_CR3/Track_1/SOE/phd_t1_soe_u06a1_h03_evaldisc.html