Clinically significant anxiety affects 20% of preschoolers and can become chronic, leading to depression, substance abuse, school-drop out and even suicide. To reduce anxiety and prevent its sequelae, clinically affected children must be effectively treated early. Available interventions for clinically anxious preschoolers are effective for some, but not all children, with as many as 50% of 4-7 year olds continuing to meet criteria for an anxiety disorder after treatment. To address this problem, we leverage theoretical models and empirical research suggesting that insufficient capacity for Effortful Control (EC) may underlie anxiety from its earliest stages. Insufficient capacity for EC reflects failures of frontal brain regions (e.g., dorsolateral prefrontal cortex/dlPFC and anterior cingulate cortex/ACC) to adaptively regulate threat circuits and maintain on-task behavior. These neural substrates for EC can be indexed using neurophysiological measures, the error-related negativity (ERN) and time frequency interchannel phase synchrony (ICPS), respectively. Findings from our labs and the work of others have shown that reduced ERN and ICPS relate to behavioral deficits in EC and enhanced threat reactivity similar to that documented in clinically anxious children. In response, our team developed a child-friendly group EC training (“Camp Kidpower”) designed to increase ERN, ICPS and related EC behaviors in the service of decreasing anxiety symptoms in preschoolers. Results of our pilot study indicate that this brief cognitive training approach engaged the intended EC neural and behavioral targets and reduced anxiety symptoms. Building on this pilot work, the current project aims to replicate and extend these findings in a larger sample using a randomized controlled design. Participants in this study will be 4- to 6-year-old children (n=90) with clinically significant symptoms who will be randomized into the EC training intervention (n=45) or a playgroup control (n=45). Outcomes will be assessed before and after each condition, using a multi-level approach that includes neurophysiological and behavioral indices of EC, as well as clinician-rated and parent- report on child anxiety symptoms (type and severity). Our aims are to: 1) confirm that participation in our EC training increases ERN and ICPS and improves EC behavior, 2) test whether engagement of these brain-behavior EC targets correspond to reductions in anxiety symptoms and explore whether anxiety reduction by EC training is moderated by baseline threat reactivity measures, and 3) identify whether greater dosage of EC training is associated with greater neuro-behavioral target engagement and reduction of anxiety symptoms. By evaluating how changes in neuroscience-derived targets relate to changes in anxiety symptoms, this work is responsive to the NIMH call for experimental therapeutics and addresses an urgent need for the design of interventions to reduce anxiety in young children.