Long responses drift away from the teacher, so the teacher rewrites the student's prefix
AspireAI community · arXiv
In on-policy distillation the student is trained on its own responses using token-level teacher feedback. As responses get longer, the student's prefix drifts from the teacher's reasoning, which weakens the feedback on later tokens - and updates based on that feedback reinforce the same drift. Existing fixes such as length control and loss reweighting limit learning from bad responses but leave the offending prefix in place, while fixed cutoffs throw away useful later reasoning. ATI-OPD replaces the earliest high-disagreement segment with a short teacher segment and lets the student resume its own reasoning from the revised text, excluding persistently divergent suffixes from the loss while retaining useful continuation. Training diagnostics show less teacher-student disagreement, fewer gradient spikes and fewer extremely long responses, and across five mathematical reasoning benchmarks and two teacher-student pairs the authors report improved average student-only accuracy over standard OPD.
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