I really like the suggestion that Shayna Sheinfeld shared in a recent article, for using word clouds in a pre-test and then post-test in classes. If you ask students what they think, or think they know, about a topic, on the first day of class or the start of a new unity, and create a word cloud from their answers, and then do the same at the end of the semester or the end of the unit, you will be able to see visually how their vocabulary has broadened, how their understanding of what is important may have shifted, and other important things, by placing the two word clouds side by side.
Below is an example from a course on Judaism.
What do you think of this idea for informal assessment? I like the way it allows the data to be visualized in a manner that is conducive for use in class, so that students can see it and benefit from it as well as the professor.