State and local educational agencies are grappling with growing mental health needs among school-aged children that intensified during the COVID-19 pandemic. We undertake a case study of the experiences of one state, Tennessee, to examine the landscape of mental health interventions that are being deployed and to illuminate contextual factors that can support their implementation or exacerbate state and local challenges in addressing children's fast-rising mental health needs. We begin with an examination of the knowledge base on interventions and approaches that are commonly employed in K-12 schools to address children's mental health needs, including in Tennessee, with the aim to identify notable gaps in what we understand about their implementation and impacts on student outcomes. We find a lack of rigorous research that can inform efforts to improve the implementation and effectiveness of school-based mental health interventions. We bring this insight to our case-study analysis, which shows that this lack of guidance from research is compounded by inadequate, time-limited and fluctuating public funding that hinders local efforts to establish strong, ongoing programs that provide or connect K-12 students to essential mental health services. We call for more federal funding to support state and local implementation of proven and promising interventions for addressing children's mental health needs and more rigorous evaluations to strengthen the evidence base on their implementation and impacts.