Cross-Corpus CEFR Classification through Artificial Learners Perplexities

Bernardo Stearns, John P. McCrae, Thomas Gaillat


Abstract
The complexity of neural methods for automatic proficiency assessment often sacrifices interpretability and robustness. This paper presents a competitive alternative for CEFR classification using optimized statistical models with a novel perplexity-based feature engineering pipeline. We introduce LLM-derived perplexity features as a proxy for how unexpected a learner’s word choices are: native model perplexity measures unexpectedness relative to native language use, while Artificial Learner model perplexity quantifies relative to a specific proficiency level. While recent work favors end-to-end neural architectures, we demonstrate that traditional pipelines enhanced with these interpretable perplexity features can achieve comparable performance on established benchmarks. We evaluate two transfer scenarios: zero-shot (trained on EFCAMDAT, tested on external corpora) and 90-10 split (same features, in-domain classifier training). On KUPA-KEYS, perplexity features achieve RMSE 0.707 (zero-shot) and 0.660 (90-10 split), outperforming fine-tuned BERT and prompt-based LLMs. On CELVA-SP, zero-shot perplexity shows limited generalization (RMSE 1.437 vs. LLM’s 1.016), but statistical models close this gap in the 90-10 split (RMSE 0.872). Across all three evaluation datasets, perplexity-based models achieve the best average macro F1 in the 90-10 split (0.446 vs. 0.287 for BERT and 0.175 for prompting), demonstrating that interpretable features paired with domain-adapted classifiers provide the most robust cross-domain representations. We contribute: (1) state-of-the-art KUPA-KEYS results with interpretable models, (2) the first comprehensive CELVA-SP benchmark, and (3) evidence that feature-level transfer outperforms both end-to-end fine-tuning and zero-shot prompting.
Anthology ID:
2026.lrec-1.62
Volume:
Proceedings of the Fifteenth Language Resources and Evaluation Conference
Month:
May
Year:
2026
Address:
Palma de Mallorca, Spain
Editors:
Stelios Piperidis, Núria Bel, Henk van den Heuvel, Nancy Ide, Simon Krek, Antonio Toral
Venue:
LREC
SIG:
Publisher:
ELRA Language Resource Association
Note:
Pages:
828–837
Language:
External URL:
https://lrec.elra.info/lrec2026-main-062
DOI:
10.63317/2bvpcczgao2t
Bibkey:
Cite (ACL):
Bernardo Stearns, John P. McCrae, and Thomas Gaillat. 2026. Cross-Corpus CEFR Classification through Artificial Learners Perplexities. In Proceedings of the Fifteenth Language Resources and Evaluation Conference, pages 828–837, Palma de Mallorca, Spain. ELRA Language Resource Association.
Cite (Informal):
Cross-Corpus CEFR Classification through Artificial Learners Perplexities (Stearns et al., LREC 2026)
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