Techniques for self-assessment

Which of the different activities/techniques for self assessment can help you the most in a classroom situation?

Questionnaires are for me the most suitable self assessment technique because it gives the students and opportunity to think about what they are going to write about.
The teacher can get to know if the student is capable of expressing his needs, of writing them correctly and of giving alternatives to work on them.
It is also a form of knowing what the students think of the class and if they think it helped them with the learning of a second language.