Study-Strategy Clusters from EdNet Logs Track Engagement, Not Mastery

Learning analytics often treats unsupervised clusters of intelligent tutoring system (ITS) logs as learner types that should predict learning. We test that assumption on EdNet-KT3. Clustering study-strategy features (resource use, revision, video, problem practice) for 5,000 active learners yields a silhouette-selected parent cut (k=5) with 4 contrast poles (reading-focused, video-heavy, revision-heavy, and problem-first) plus a large near-mean residual (~64.9%). Reclustering that residual adds four finer styles, giving a bootstrap-stable hierarchy of 8 named strategies. We split each learner's timeline by respond count so clusters use only the early half and outcomes only the late half. Early clusters predict later engagement (continuing to practice and finishing late sessions, especially persistence, η2≈ 0.106; completion η2≈ 0.021) but not later unassisted accuracy (correctness on late first-attempts without help; padj≈ 0.093). Volume rises with some styles, yet volume-only clustering barely matches strategy labels (ARI=0.064). A knowledge-tracing model (SAKT) on the seven TOEIC exam sections predicts next correctness only modestly better than a baseline that knows only how hard each section usually is (AUC lift +0.051; CI [+0.045,+0.058]), and that mastery signal is nearly independent of behavior styles (ARI=0.007). Behavioral clustering here describes study styles and engagement, not knowledge gains.