Tracking one student has its advantages. When you are working with a group of students, it’s hard to notice what each one is acquiring. My single student surprises me, as did my former one, by knowing/recognizing/using words that had not loomed large in the narrative nor been repeated. It makes me wonder about the TPRS dictum that 80 reps are necessary for acquisition.
That makes sense, but there yet remains this phenomenon of what appears to be random acquisition beyond the expected. An example today was the Spanish word choza, meaning hut. It occurred several months ago and only in connection to a particular character in the narrative. I would have to check my scripts but I think it may have occurred only in one episode.
What might account for its acquisition? Two things: a picture accompanied the word and the setting and action were dramatic.
That has been my theory, based prior to this single-student teaching experience on my own learning experience. A word will stick with me and often it can be related to a salient usage in a powerful context.