Background/Context: The U.S has experienced years of lost progress in math because of the COVID-19 pandemic (NAEP, n.d.a). Fraction understanding is widely characterized as the gatekeeper to algebra (Booth et al., 2012; National Mathematics Advisory Panel, 2008) and can support success in middle and high school math (Bailey et al., 2012; Booth et al., 2014; Siegler et al., 2012; Powell et al., 2019). Supporting fraction understanding in upper elementary and middle school may be a way to accelerate students' math learning and recovery. Fraction Face Off (FFO) is an intervention which promotes fraction understanding in grade 4 and has promising evidence to improve math outcomes for students experiencing math difficulty (IES, 2020; Fuchs et al., 2013). This study is funded by a mid-phase Education Innovation and Research grant to explore whether FFO results can be replicated and scaled to more grades. Purpose/Objective/Research Question: The questions examined through this evaluation include: 1. What is the impact of FFO on grade 4 students' fractions knowledge, general math knowledge, efficacy and anxiety? 2. Does implementing FFO increase interventionist' fractions knowledge and efficacy? Setting: Interventionists and grade 4 students from public schools in Missouri and Texas. Population/Participants/Subjects: 61 interventionists and 300 students with math difficulty participated in the study and had at least one outcome measure. Student eligibility was determined via a screening process. Students with an identified learning disability and IEP goals in math and who scored below the 35th percentile on the WRAT-5 were eligible. The overall and differential attrition for interventionists and their students were low and met acceptable levels of potential bias (IES, 2022). Intervention/Program/Practice: FFO includes 36 sessions divided into a 12-week schedule, with 3 sessions per week, each lasting about 30-35 min. Interventionists received 3 days of professional development. The Content and Pedagogy Training was held in-person and during the school day. The training included an introduction to the theory behind teaching fractions, a review of best practices for teaching students who are struggling with math, and an overview of FFO content. Interventionists were also provided with six "just in time" trainings throughout the 12-week implementation period. The trainers modeled delivery of up to 6 of the 36 lessons during these training. Trainers observed each interventionist four times during the implementation period and provided supplemental coaching as needed. Interventionists could implement the program anytime prior to state testing in the spring. Research Design: We used a randomized experiment to examine the impact of FFO. The 61 interventionists were block-randomized to either implement or not implement FFO during the 2022-23 school year. Blocks were learning community (e.g., schools, district, state) and included a minimum of two teachers. Data Collection and Analysis: The implementation team collected student and interventionist fraction knowledge, general math knowledge, efficacy and anxiety data prior to and directly after implementation of FFO during the 2022-23 school year. The fractions knowledge measures administered to students included the Vanderbilt fraction battery (Schumacher et al., 2013), and fraction number line (Siegler et al., 2011). The general math knowledge measures administered to students included the wide range achievement test-5 (Wilkinson & Robertson, 2017), Stanford achievement test-10 procedures and problem solving (Pearson, 2007), and state standardized assessments in mathematics. Measures of student math anxiety (Bai, 2011) and math efficacy (Umay, 2001) were also collected. The fractions knowledge measures administered to interventionists included compare to 3/5 (Schneider & Siegler, 2010), fraction number line (Schneider and Siegler, 2010), and rational number knowledge test (Powell, Gilbert, & Fuchs, 2019). A survey was used to collect interventionist perceptions of self-efficacy using the MTEBI (Enochs, Smith, and Hunker, 2000). The efficacy of the FFO intervention on student outcomes was analyzed using mixed effect regression models (students nested in interventionists) and the impact of FFO on interventionist outcomes was analyzed using OLS regression. All models included the baseline measure and the necessary design elements (treatment indicator, dummy variables for randomization block, interventionist random effects, individual baseline measure, cluster-aggregate baseline measure). Missing outcome data was not imputed. We used case-deletion (complete case analysis) for baseline and outcome measures, limiting the inference sample to students and interventionists with both measures. Missing covariate data were handled via a dummy variable approach. Model covariates were determined via an iterative elimination procedure. Additional covariates included gender, race/ethnicity, special education status, English language learner status, and free/reduced price lunch status. Findings: Appendix B provides the estimate of FFO impacts. Students: There was a large, significant positive effect of FFO on the fraction arithmetic measure (ES = 1.06) and marginally significant improvements in fraction magnitude comparison and ordering fractions (ES = 0.26 and 0.25). There were no notable differences in performance between students on the fraction understanding and fraction number line assessments. There was a small, marginally significant effect of FFO on state assessment scores (ES = -0.20). There were no notable differences in performance between students on the other general math measures. FFO had a positive impact on student math efficacy (ES = 0.33) and there was a small, non-significant increase in math anxiety for FFO students (ES = 0.10). Interventionists: FFO interventionists performed similarly on fraction assessments compared to control interventionists with one notable exception. There was a negative effect of FFO on interventionist performance on Compare 3/5 (ES = -0.39). This was due to a large increase in scores from pre to post for control teachers coupled with a slight decline in scores for FFO teachers. Additional information is needed to understand why this might be occurring. FFO interventionists reported a similar sense of efficacy prior to and following implementing FFO during the school year. Whereas, control teachers, on average, reported a slight drop in efficacy from fall to the spring. The effect between study conditions was small and non-significant (ES = -0.13). Conclusions: FFO is a promising intervention for developing grade 4 students' math efficacy and fraction arithmetic skills. While the findings from Fuchs et al (2013) were not fully replicated, there may be several factors influencing replication including differences in sample, implementation team and measures used.