Here are my best and worst experiences about the assessment.
In my undergrad, in most of the courses, the assessments were used only to rank students! No feedback and comments were provided after exams. Almost in all courses, we had one midterm and one final exam and the instructors only announced the grades. I remember I studied very hard for a test and after the test, I was almost sure that I will get the full grade. However, I got 15 from 20. I went to the instructor office and asked him about my mistakes. He said I can review your answers but, this time, I am sure you will get less than 15! I never found what were my mistakes in that course.
Assessment should be used to motivate students to study (I study more when I have an exam) and give them feedback about their understanding. However, it was not the case in my undergrad.
My best experience about the assessment happened last fall. At the first day, the instructor explains the main goals of the course and handed in 2 pages to the students. Ninety-nine concepts were listed on the pages. He said you should be familiar with these ninety-nine concepts at the end of the course. In the beginning of each session, he explained which concepts will be reviewed in the session. He also sometimes explained that we have learned, for example, 20 of the listed concepts, if you did not learn some of them, please come to my office and ask me about them. All the exams and quizzes were about the listed concepts and we already know which concepts will be on each test. The most interesting part of the assessment was his feedbacks. Sometimes I thought I know a concept very well. However, after the test, he wrote some comments about my misunderstandings and at the end which concept I should learn better. I always was eager to take his tests because they were not for grading; the tests were a tool to evaluate our understandings and help us to eliminate our weaknesses.