Purpose <p>Outcomes after brachial plexus birth injury (BPBI) vary widely, highlighting the need for rehabilitation strategies that reliably enhance functional recovery. We hypothesized that a coordinated, interdisciplinary rehabilitation network involving surgeons and occupational therapists improves functional outcomes after spinal accessory to suprascapular nerve (SAN-SSN) transfer. We compared outcomes from two academic centers with similar surgical indications and techniques but distinct rehabilitation models.</p> Methods <p>We reviewed 25 infants who underwent SAN-SSN transfer from 2022 to 2024. Institution A used a coordinated multidisciplinary rehabilitation model in which the surgeon partnered directly with specialized therapists. Patients at institution B self-selected therapy sites. Pre- and postoperative external rotation Active Movement Scale (AMS) scores were collected and analyzed.</p> Results <p>Both cohorts showed significant improvement in external rotation (ER) (<i>P</i> &lt; 0.05). Median postoperative AMS scores were higher at institution A (7; interquartile range [IQR] 5.5–7) than at institution B (4; IQR 3–5). Functional recovery (AMS ≥ 6) occurred in 72.7% of institution A patients versus 14.3% at institution B (<i>P</i> = 0.005). Within institution B, on-site therapy produced significantly better outcomes than off-site therapy. Patients at institution A had 11.8-fold greater odds of achieving higher AMS scores than patients at institution B (<i>P</i> = 0.018); these differences were not significant when comparing institution A to institution B’s on-site subgroup.</p> Conclusions <p>Surgeon-directed, expert-guided therapy is associated with superior recovery after SAN-SSN transfer for BPBI. These findings support the impact of a scalable model which prioritizes timely, consistent, and coordinated postoperative rehabilitation.</p> Level of Evidence: <p>III, retrospective cohort comparison.</p>