The teacher and the student

In order for a teacher to check the student's understanding, then the teacher needs to get the student to do something or some things that illustrate the student's understanding. In this way both the student and the teacher can be sure that understanding has occurred. For example, if a teacher has taught a student a new word, the teacher might ask the student to define the word. If the student can define the word, then the teacher may be happy the student has the knowledge. The teacher might ask the student to use the word in a few sentences, and if the student uses the word meaningfully, then the teacher might be happy that the student understands the word to some degree. If the teacher notices that the student is using the word in everyday life, then the teacher may be happy that the student has understood the word.