<p>When assessing student skills, accurate judgment is essential for effective teaching; however, teachers’ competence in doing so (assessment competence) can be compromised by the availability of non-diagnostic cues. This study investigates how various cue types and cue-related information affect teachers’ accuracy in making judgments within the specific context of assessing self-regulated learning (SRL). Participants (<i>N</i> = 263) were divided into three groups: one received only diagnostic cues (e.g., students’ use of elaboration strategies, <i>n</i> = 83); another had access to both diagnostic and non-diagnostic cues (e.g., handwriting, social school reports, <i>n</i> = 84); and a third group received both types of cues along with explicit information about the low diagnostic value of certain cues (<i>n</i> = 96). Findings showed that judgment accuracy was highest when only diagnostic cues were available, and accuracy declined when non-diagnostic cues were introduced. This was consistent across different levels of teachers’ content knowledge. These results demonstrate that the difficulty of distinguishing relevant from irrelevant cues—previously observed in other judgment domains—also occurs in the context of SRL assessment, highlighting the importance of fostering teachers’ assessment competence in this area.</p>