TACTutor
TACTutor is a 4B-parameter conversational English tutor from TACT (Taxonomy-Aligned Conversational Tutor). Starting from Qwen3.5-4B-Base, the model was post-trained with supervised fine-tuning (SFT) followed by taxonomy-aligned Group Relative Policy Optimization (GRPO). It is distributed as a merged Hugging Face Transformers model rather than a LoRA adapter.
- TACT organization: https://huggingface.co/Taxonomy-Aligned-Conversational-Tutor
- Demonstration samples: https://huggingface.co/datasets/Taxonomy-Aligned-Conversational-Tutor/TACTBench-Samples
Intended Use
TACTutor generates the next teacher response in an ongoing English-learning conversation. It is intended for research on pedagogically adaptive dialogue, including feedback, guided revision, clarification, and learner-supportive conversation management.
The model is a research artifact, not a replacement for a qualified teacher. Outputs should be reviewed before use in high-stakes educational settings.
Loading
from transformers import AutoModelForCausalLM, AutoTokenizer
model_id = "Taxonomy-Aligned-Conversational-Tutor/TACTutor"
tokenizer = AutoTokenizer.from_pretrained(model_id, trust_remote_code=True)
model = AutoModelForCausalLM.from_pretrained(
model_id,
torch_dtype="auto",
device_map="auto",
trust_remote_code=True,
)
One prompt used in our evaluation is:
You are an expert ESL tutoring teacher.
Your job is to write the next teacher response in an ongoing teacher-student chat.
Respond naturally and pedagogically. Do not explain your reasoning. Do not mention
taxonomy labels, rubrics, or evaluation criteria.
Pass this instruction as the system message, followed by the dialogue history, and use the tokenizer's chat template to construct the model input.
Evaluation
On the 78-item TACTBench diagnostic benchmark, the selected checkpoint achieved:
| Metric | Score |
|---|---|
| TACT Overall | 0.832051 |
| Accept | 0.871795 |
| Leak | 0.025641 |
| Off-task | 0.025641 |
The scores above were measured before five representative benchmark examples were released. Those public examples are demonstration data and should be excluded from future hidden-set scoring.
Training Data and Limitations
The post-training data are derived from authentic English tutoring dialogue and taxonomy-guided augmentation. The complete training corpus and hidden benchmark are not included in this repository. Five short full-context demonstration examples are available in the companion dataset repository.
The source dialogue is derived from the Teacher-Student Chatroom Corpus version 2 (TSCC v2), which is governed by its own user agreement. This model may produce incorrect, overly explicit, or contextually inappropriate tutoring responses, and its behavior outside English-language tutoring has not been established.
Citation
Please cite the following paper when using TACTutor:
@article{yang2026tact,
title = {TACT: Taxonomy-Aligned Post-Training for Pedagogically Adaptive English Tutoring},
author = {Yang, Dongjie and Lin, Siyan and Shen, Leixian and Sheng, Rui and Qu, Huamin and Chen, Zixin},
year = {2026}
}
License
The model weights are released under the Apache License 2.0. The TSCC-derived source data remain subject to the TSCC user agreement and are not redistributed with the model weights.