A dictation is a good way for students to practicing their writing and is also helpful for teaching grammar. It is suggested that you use a story that was told in the previous class, so that the subject matter for the writing is not random. This boosts students’ confidence and since they know the basic story, it is easier for them to follow. It is also often a nice break from stories.
Basically the teacher says one phrase or chunk of the story aloud. Say each part of the phrase three times, slowly enough so that the students have time to write it. Include punctuation instructions in the target language. Students then write what they hear down on the first line (out of three lines). This is not actually graded, but tell students to make their best effort. Once everyone has at least made an attempt to write down the phrase, the teacher writes it correctly on the board so that the students can compare it with their own. Any corrections they need to make go on the second line, and the third line should be left blank so the page doesn’t get too crowded.
The dictated version of the doesn’t have to be perfectly accurate. You can even make intentional errors as you tell it to force deeper thinking by the students. During the process, students will want to talk, but it is better if they stay silent and the teacher stays in the target language the entire time. Since students who wrote the line perfectly and don’t need any corrections want everyone else to know, you can have them give some kind of sign to show they did it, like raising their hand or making a swooping motion with one hand. The teacher can then acknowledge those students with positive comments in the target language.
After the dictation is complete, you can talk about the grammar for a short time (five to seven minutes). And finally you can have the students read chorally and then individually.
Source: Ben Slavic, Ben Slavic on Comprehensible Input