Teachers are critical partners in expanded school mental health (ESMH) collaborations that aim to bring educators, community mental health professionals and families together to leverage expertise and resources for addressing non-academic barriers to learning. Although teachers are in a unique position to observe the day-to-day mental health needs of students, their roles in ESMH collaborations have been largely ignored leaving little research-based guidance for maximizing this practice strategy. To address this gap, this study explored 384 teachers' experiences with ESMH collaboration including the types of collaborations they are engaged in, what influences those relationships and what they perceive to be the benefits of this practice strategy. The findings support previous conceptual and research contributions focused on collaboration, as well as suggest some specific influences on collaborative relationships between teachers and community mental health professionals. Implications for practice, policy and research are offered.