Growth teams reach for acquisition channel when week-two retention slips. Curriculum leads reach for lesson difficulty. Both can be right — but only lesson-level cohorts tell you which.
In a typical Sitecornerhub audit we rebuild cohorts by first lesson completed, then overlay the first failed skill checkpoint. For grammar-heavy paths, the cliff often appears after the first multi-tense unit or tone drill, even when payment conversion looks fine.
Practical steps:
- Exclude learners who never finished lesson one; they are acquisition waste, not pedagogy signal
- Mark intentional exercise attempts separately from autoplay listening
- Interview five learners who stopped after the cliff unit before rewriting the entire path
If your warehouse cannot slice by lesson ID cleanly, fix naming before commissioning another acquisition experiment. The retention audit exists for that inventory work.