National interest is growing in Integrated Student Support (ISS) interventions, which offer schools systematic ways to reduce barriers to learning. The present study exploits the random component embedded within the school assignment system of a large urban school district to estimate the effect of schools providing ISS on student academic achievement at third, fourth, and fifth grade. The sample included students (N = 2,342) randomly assigned to schools--with or without ISS--via enrollment lottery. Students assigned to schools implementing ISS demonstrated higher achievement (from approximately 0.02% to more than 50% of a standard deviation) than those assigned to control schools. While we found some evidence for the efficacy of ISS by third grade, treatment effects were consistently largest and proved most robust across modeling strategies at fifth grade. The practical significance of these findings is discussed with attention to ongoing national efforts to improve the learning opportunities of economically disadvantaged students.