While traditionally most faculty think of assessing or reflecting upon their courses when they are finished, it is also helpful to think about assessment issues during the course. While there are many reasons to assess courses one of the most prominent techniques is assessing students to help identify and intervene if there are serious issues. This technique can be especially useful when trying to increase retention and graduation rates of students (particularly students from underserved backgrounds).
Secondly, teachers may also want to gauge the overall feeling of the students or identify which parts of their teaching are working or not working for students. While some faculty may be uneasy with opening up discussion of the process as a class is going, many faculty have found it to be a useful tool to help improve learning outcomes, understand their teaching and possibly course correct for a better overall class.
Below are some resources for mid-semester evaluations
A faculty member's experience with mid-semester evaluations
The CSUSM TrioStudent Support Services offers support for mid-semester evalautions and early interventions