<p>Although frequently used with instructional expository text, it has been suggested that illustrations can lead to illusions of understanding (beliefs that we understand better than we actually do). In this study using geoscience texts, relative metacomprehension accuracy (the ability to monitor one’s own understanding across a set of topics) was found to be particularly poor when only some topics were illustrated. However, when readers were prompted to generate sketches while reading, relative accuracy was improved, and was more similar across illustration conditions. Consistent with the situation-model approach to metacognition, sketching activities may help readers to generate valid and diagnostic cues on which to base their judgments of understanding and avoid reliance on heuristic cues or superficial processing.</p>