Classroom Assessment Techniques (CAT's) are formative and/or summative assessments to determine what the student currently knows and what the students have learned. It can identify gaps in learning. CAT's must be chosen carefully and align with the objectives and goals of the course. Some examples of CAT's would be: a one-minute paper and Muddiest Point.
Personally, I have found entrance quizzes to be effective. This helps the students to identify what knowledge they have gained prior to class time. At the end of the class, the students review the content from the quiz to identify areas they need to still review.
