Repair of partial or transitional atrioventricular septal defects (P/TAVSDs) has excellent outcomes; however, late reinterventions remain a concern. Technical performance score (TPS) measures residua after repair and has been associated with early/mid-term outcomes after congenital cardiac operation. Our study investigates TPS as a predictor of outcomes after P/TAVSD repair. This was a single-center retrospective review of P/TAVSD repair from July 2000 to November 2015. Intraoperative and discharge TPS were assigned based on echocardiographic criteria: class 1, no residua; class 2, minor residua; and class 3, major residua or reintervention for major residua. Intensive care unit (ICU) hospital length of stay and reintervention after discharge were analyzed with Cox regression. In our cohort, 124 partial (68%) and 59 transitional (32%) AVSDs underwent repair. Median age was 1.5 years (interquartile range IQR: 0.6 to 3.8 years), median weight was 9.7 kg (IQR: 6.6 to 14.1 kg), and 96 (52%) were female. Twenty patients (11%) required reintervention after discharge. On multivariable modeling, patients with TPS class 3 spent more days in the ICU (hazard ratio HR 0.33, 95% confidence interval CI: 0.19 to 0.58, p < 0.001) and hospital (HR 0.33, 95% CI: 0.19 to 0.57, p < 0.001) and had shorter time to reintervention after discharge (HR 8.76, 95% CI: 1.03 to 74.7, p = 0.047). Major residua, that is TPS class 3, were a predictor of in-hospital outcomes and unplanned reinterventions after discharge, with left atrioventricular valve regurgitation being the strongest predictor. Use of TPS as a tool for residual lesions may identify patients predisposed to prolonged ICU hospital stay and reinterventions after discharge, providing feedback on areas in need of improvement in technique and identification of patients who warrant closer follow-up. Display omitted