IMPORTANCE Despite the high level of impairment for adolescents with persistent postconcussive symptoms, few studies have tested whether such problems can be remediated. OBJECTIVE To examine whether collaborative care treatment is associated with improvements in postconcussive, quality of life, anxiety, and depressive symptoms over 1 year, compared with usual care. DESIGN, SETTING, AND PARTICIPANTS The Collaborative Care Model for Treatment of Persistent Symptoms After Concussion Among Youth II Trial was a randomized clinical trial conducted from March 2017 to May 2020 with follow-up assessments at 3, 6, and 12 months. Participants were recruited from pediatric primary care, sports medicine, neurology, and rehabilitation clinics in western Washington. Adolescents aged 11 to 18 years with a diagnosed sports-related or recreationalrelated concussion within the past 9 months and with at least 3 symptoms persisting at least 1 month after injury were eligible. Data analysis was performed from June to September 2020. INTERVENTIONS The collaborative care intervention included cognitive behavioral therapy and care management, delivered mostly through telehealth, throughout the 6-month treatment period, with enhanced medication consultation when warranted. The comparator group was usual care provided in specialty clinics. MAIN OUTCOMES AND MEASURES Primary outcomes were adolescents' reports of postconcussive, quality of life, anxiety, and depressive symptoms. Secondary outcomes were parentreported symptoms. RESULTS Of the 390 eligible adolescents, 201 (51.5%) agreed to participate, and 200 were enrolled (mean [SD] age, 14.7 [1.7] years; 124 girls [62.0%]), with 96% to 98% 3-to 12-month retention. Ninety-nine participants were randomized to usual care, and 101 were randomized to collaborative care. Adolescents who received collaborative care reported significant improvements in Health Behavior Inventory scores compared with usual care at 3 months (3.4 point decrease; 95% CI, −6.6 to −0.1 point decrease) and 12 months (4.1 point decrease; 95% CI, −7.7 to −0.4 point decrease). In addition, youth-reported Pediatric Quality of Life Inventory scores at 12 months improved by a mean of 4.7 points (95% CI, 0.05 to 9.3 points) in the intervention group compared with the control group. No differences emerged by group over time for adolescent depressive or anxiety symptoms or for parent-reported outcomes.