Since its introduction in the late 1990s, the unskilled and unaware effect motivated several further studies. As it stands, low-performing students are assumed to provide inaccurate and overconfident performance judgments. However, as research with second-order judgments (SOJs) indicates, they apparently have some metacognitive awareness of this. The current study with 266 undergraduate students aimed to provide in-depth insights into both the reasons for (in)accurate performance judgments and the appropriateness of SOJs. We implemented a general linear mixed model (GLMM) approach to study item-specific performance judgments in the domain of mathematics at the person and item level. The analyses replicated the well-known effects. However, the GLMM analyses revealed that low-performing students' lower confidence apparently did not indicate subjective awareness, given that these students made inappropriate SOJs (lower confidence in accurate than in inaccurate judgments). In addition, students' self-generated explanations for their judgements indicated that low-performing students have difficulties recognizing that they possess topic knowledge to solve an item, whereas high-performing students struggle with admitting that they do not know the answer to a question. In sum, our results indicate that students at all performance levels have some metacognitive weaknesses, which, however, occur subject to different judgment accuracy.