  Student assessment is one of the most fundamental tasks in the field of AI
Education (AIEd). One of the most common approach to student assessment is
Knowledge Tracing (KT), which evaluates a student's knowledge state by
predicting whether the student will answer a given question correctly or not.
However, in the context of multiple choice (polytomous) questions, conventional
KT approaches are limited in that they only consider the binary (dichotomous)
correctness label (i.e., correct or incorrect), and disregard the specific
option chosen by the student. Meanwhile, Option Tracing (OT) attempts to model
a student by predicting which option they will choose for a given question, but
overlooks the correctness information. In this paper, we propose
Dichotomous-Polytomous Multi-Task Learning (DP-MTL), a multi-task learning
framework that combines KT and OT for more precise student assessment. In
particular, we show that the KT objective acts as a regularization term for OT
in the DP-MTL framework, and propose an appropriate architecture for applying
our method on top of existing deep learning-based KT models. We experimentally
confirm that DP-MTL significantly improves both KT and OT performances, and
also benefits downstream tasks such as Score Prediction (SP).
