Literacy skills are instrumental to unlocking a child's full potential and have a well-established link to long-term life outcomes. Children who can't read at grade level by 3rd grade are four times more likely to drop out of school, have fewer career prospects, and earn lower incomes as adults. However, despite some progress on literacy rates, almost 40% of Chicago Public Schools (CPS) students entering 9th grade still lack basic reading proficiency. Now in high school, these students are running out of time to successfully gain the literacy skills they need to graduate and thrive. Most reading interventions are focused on elementary schoolers, so there are few structured literacy opportunities available to older students, let alone interventions that can accelerate their learning enough for them to close the gap. With their pathway to literacy narrowing, it's crucial that we provide them with the urgent, intensive support they need. To fill this gap, in 2020, CPS started rolling out the Structured Literacy program to engage high schoolers with the highest need of literacy support in a robust reading intervention that focuses on decoding and encoding text. The program features small-group, individualized instruction in a separate class period. Students with similar literacy needs are grouped together to receive personalized daily instruction that incorporates evidence-based practices using the Wilson Reading System (WRS). In these sessions, the program provides opportunities for students to read culturally relevant texts at their level, augmenting a skill-based reading curriculum with age-appropriate general texts to enhance engagement. Sessions are integrated into the school day and students earn course credit as part of their high school schedule. We study the impact of the Structured Literacy program using a multi-year randomized controlled trial (RCT) starting in SY2020-21 to SY2023-24. We randomized over 2,700 students across 13 CPS high schools to either receiving the Structured Literacy program or a control condition. Preliminary findings from analysis of the first 3 cohorts suggest the program increased reading scores by 0.20 standard deviations.