This study explored how elementary teachers leveraged and structured student-involved formative assessment to promote metacognition and self-regulation. Research has suggested a connection between formative assessment practices (e.g., self-assessment and peer-assessment) and metacognition. However, this connection has limited empirical support, especially within early elementary contexts (i.e. Grades K-4). In this study, 44 Ontario elementary teachers completed a survey reporting their teaching and assessment practices and beliefs about metacognition. Five participants were then purposefully selected for semi-structured interviews to describe their experiences developing students' metacognition and self-regulatory capabilities through student-involved assessment processes. Data were inductively and thematically analysed. Participants emphasized the value of "assessment as learning" practices (e.g., self-assessment and reflective thinking) to develop students' metacognition and discussed the need for ongoing student feedback regarding metacognitive strategies. However, despite purposefully implementing formative assessment to enhance metacognition and self-regulation, participants articulated the need for additional resources to support the cultural shift towards assessment "for" and "as" learning within their classrooms.