Math self-competence beliefs, namely, math self-efficacy and math self-concept, are crucial factors in sustaining math learning. Since there is a lack of literature on interventions targeting math self-competence beliefs in middle school students, the aim of this systematic review is to provide a narrative synthesis of the characteristics of interventions focusing on math self-efficacy and math self-concept in middle school students, and to describe their effects in enhancing math outcomes. A total of 15 intervention studies met the inclusion criteria (i.e., studies conducted on middle school students, interventional or quasi-experimental, studies evaluated math self-efficacy and math self-concept), comprising a sample of N = 10,416 middle schoolers and n = 21 effect sizes. Qualitative analysis identified five main types of interventional approaches: self-regulation strategies (n = 3), use of technology (n = 3), instructional teaching (n = 3), enhancement of self-competence sources (n = 3), and collaborative learning (n = 3). Collaborative learning and technology-based interventions seemed effective in enhancing students' math self-competence beliefs. Conversely, interventions focusing on self-regulation strategies, as well as instructional teaching, appeared more effective in improving math outcomes than self-competence beliefs. These findings provide valuable insights for educational practitioners and policymakers, informing evidence-based choices for optimizing teaching practices and intervention activities in educational context.