Streaks are easy to instrument and hard to interpret. A learner who opens the app for a thirty-second vocabulary flash still “keeps” a streak, while someone who skips a day after a ninety-minute speaking session looks like a failure in the chart.
In retention audits we ask teams to pair streak length with return after break: the share of learners who complete a meaningful exercise within seven days of a broken streak. If that rate is healthy, streaks are a reminder layer. If it is weak, the streak is theatre.
Also separate calendar opens from exercise completions. Language learning apps that celebrate opens often hide unfinished drills. Your curriculum authors already know the difference; your event names should too.