Objective: Research has demonstrated the effectiveness of interventions to reduce organizational skills deficits and homework problems, including the clinic-based Organizational Skills Training (OST-C) program (Abikoff et al., 2013). In this study, OST-C was adapted for schools as a small-group (Tier 2) intervention delivered by school partners (OST-T2). Method: The study was conducted in 22 schools serving students from diverse backgrounds. Students (n = 186; 122 male) in grades 3-5, ages 8-12 (M = 9.7 years; SD = 0.88) with organizational skills deficits referred by teachers were enrolled. Schools were randomly assigned to OST-T2 or treatment-as-usual with waitlist (TAU/WL). OST-T2 consisted of sixteen 35-minute child sessions, two caregiver, and two teacher consultations. Outcomes were evaluated with longitudinal mixed effects modeling at post-treatment, 5-month and 12-month follow-up using caregiver and teacher reports of organizational skills, homework, and academic performance. Results: OST-T2 resulted in reductions in organizational skills deficits on caregiver and teacher report (ps < 0.001) at post-treatment and 5-month follow-up (effect sizes [ES], Cohen's d = 0.96,1.20). Findings also revealed a reduction in caregiver-reported homework problems at post-treatment and 5-month follow-up (ps < 0.001, ES = 0.60, 0.72), and an improvement in teacher-rated homework at post-treatment (p = 0.007, ES = 0.64). Effects were attenuated at 12-month follow-up. The effects of OST-T2 on academic measures were not significant. Conclusions: Findings provide evidence for the immediate and short-term effectiveness of OST-T2 delivered by school professionals. [This paper will be published in the "Journal of Consulting and Clinical Psychology."]