<p>Predicting how well they will perform or have performed in a task – i.e., metacognitive monitoring—can allow students to engage in self-regulation during learning. Research has demonstrated that students are often prone to overconfidence and underconfidence biases however, and it remains unclear whether teachers can use simple pedagogical tools to help students (re)calibrate their metacognitive monitoring directly in the classroom. Here, we test the efficacy of a 3-step intervention that consists in routinely asking students to predict their ability to conduct a cognitive task, to retrospectively evaluate their performance, and finally, to compare their metacognitive judgments with their actual performance. We tested the efficiency of this intervention in a large-scale training study. In a test group (<i>N</i> = 297, 2nd to 12th grade), students used a metacognitive tool that allowed them to report their confidence before performing a learning task, after performing it, and after receiving feedback on their performance. In a control group (<i>N</i> = 278), students performed an equally engaging, non-metacognitive task. Predictive metacognitive monitoring improved in the test group, especially for the most vulnerable students. By contrast, retrospective metacognition did not improve. Using the tool did not improve academic outcomes in the test group compared to the control group; potential explanations for this are discussed. Our findings suggest that using simple metacognitive tools as part of regular pedagogical practices has the potential to enhance vulnerable students’ metacognitive monitoring, but that this might not be sufficient to help them improve their academic performances.</p>