An online peer-assessment system typically allows students to give textual feedback to their peers, with the goal of helping the peers improve their work. The amount of help that students receive is highly dependent on the quality of the reviews. Previous studies have investigated using machine learning to detect characteristics of reviews (e.g., Do they mention a problem, make a suggestion, or tell the student where to make a change?). Machine-learning approaches to peer-assessment evaluation are heavily reliant on labeled data to learn how to identify review characteristics. However, attaining reliable labels for those characteristics is always time-consuming and labor-intensive. In this study, we propose to apply pseudo-labeling, a semi-supervised learning-based strategy, to improve the recognition of reviews that detect problems in the reviewed work. This is done by utilizing a small, reliably labeled dataset along with a large unlabeled dataset to train a text classifier. The ultimate goal of this research is to show that for peer assessment evaluation, we can utilize both unlabeled and labeled datasets to obtain a robust auto-labeling system and thereby save much effort in labeling the data.