1. At the end of the class, I have each student write down 3 things they learned newly in that class on a piece of paper, and turn in before they leave the class.
2. After class, I look at all paper from students, and see what they understand and what they struggle with. I planned the next class according to the result.
This is a method not only for teachers to assess students , but also for students to reflect on what they learned in that class, which strengthens their retaining. It also takes at most five minutes. It is a simple effective method.