Informal writing activities of several kinds can stimulate student's private reflection and focus their thinking. As a result, these activities are often used as a springboard for in-class discussion.
Informal writing comes in many forms, some examples of which appear below. It can be helpful to make prompts very specific: instead of asking students to just "spend some time writing," ask them to write what they thought was the best or worst part of something, the most or least important, the clearest or most-confusing, the most or least useful to them, and why.
As described by Angelo and Cross (1993), minute papers are Classroom Assessment Techniques which allow you to get a fast, ungraded look at your students' thinking. As the name suggests, minute papers are quickly-written student responses to some prompt from the teacher, which the student writes in class--ideally in only about a minute.
"Minute papers" can be used as a springboard for discussion at the beginning of class, as a mid-class pause for reflection, and as an end-of-class diagnosis of how well the class session succeeded in accomplishing its objectives.
"Muddiest Point" minute papers are a very common form end-of-class diagnosis. When asking students to describe what they experienced as the 'muddiest point'-that is, the point in class which was the most confusing to them- you require them to reflect upon what they did and did not understand.
If taking roll is important, minute papers can be an unobtrusive and instructional way to do it: have students put their names on their paper and leave them in a box by the door on their way out of class.
From Angelo, T.A. & Cross, P.K. (1993). Classroom assessment techniques (2nd ed.). San Francisco: Jossey-Bass.
Like the similarly-named Think-pair-share, the Write-pair-share exercise demands that students spend a few moments writing in response to a teacher's prompt, and then have some time to discuss with their classmates before re-convening as a whole class for discussion.
Note: Again, the prompt for the Share phase of this activity should be very specific: ask students to identify the most important commonalities/differences in what they wrote, to prioritize the points the collectively made, or to clarify things about the material that their partner identified as confusing in their writing.
Freewrites can be used at similar times and for similar reasons as minute papers, but the difference is that freewriting demands that the students' pen or pencil never stop moving during the allotted time. Even if all they write is "I can't think of what to write, I can't think of what to write, I can't think of what to write," eventually the tedium of not having anything new to write will motivate them to begin thinking about the subject and generating new ideas. These short freewrites can then be discussed or the class can move ahead
One precaution: Because we are conditioned to be self-conscious about what we write and to monitor our writing in "real time," freewriting can be an exhausting experience. Do not overuse this technique.