Accurate monitoring of performance in problem-solving tasks is an important prerequisite for students' future academic success. A wide variety of interventions aiming to enhance students' monitoring accuracy have been developed, but their effectiveness is not apparent from the individual studies in which they have been examined. This meta-analysis classified these interventions in terms of how they target students' monitoring and investigated their relative effectiveness to improve monitoring accuracy in problem-solving tasks. Findings across the 35 included studies indicated that all interventions combined have a small positive effect on students' monitoring accuracy (g = 0.25). Intervention type moderated the findings. Interventions on the whole task, metacognitive knowledge, and external standards improved monitoring accuracy. On the other hand, interventions targeting the timing of metacognitive judgment negatively impacted monitoring accuracy and significantly differed from all other interventions. Exploratory moderator analyses of study features indicated that secondary school students benefited least from the interventions compared to primary school students and adults, laboratory studies showed larger effects than classroom studies, and interventions were more effective for retrospective confidence judgments than for judgments of learning. For educational practice, interventions targeting the whole task, metacognitive knowledge, and external standards are recommended, while reconsideration and possibly discontinuation of timing interventions is needed.