Background In adults with large‐vessel occlusion stroke, the extent of the baseline infarct measured using the Alberta Stroke Program Early Computed Tomography Score (ASPECTS) predicts outcome and is used during patient selection for mechanical thrombectomy. The relationship between ASPECTS and clinical outcome is unknown in pediatric large‐vessel occlusion stroke. Methods Secondary analysis of a retrospective multicenter case–control study assessing mechanical thrombectomy versus medical management alone for pediatric large‐vessel occlusion stroke across 5 centers in Australia and Canada from 2011 to 2022. ASPECTS was measured on baseline computed tomography or magnetic resonance imaging–diffusion‐weighted imaging while blinded to clinical outcome and treatment status. The relationship between ASPECTS and pediatric modified Rankin scale scores at 3 months following stroke was assessed using ordinal logistic regression. Results In total, n = 24 thrombectomy patients (F = 10, mean age, 11.3 years [SD, 4.36]) and n = 24 control patients (F = 10, mean age, 10.2 years [SD, 4.32) were included. Mean ASPECTS was 6.3 (SD, 2.37) in the thrombectomy group and 6.1 (SD, 2.64) in the control group. In patients undergoing thrombectomy, baseline ASPECTS significantly correlated with pediatric modified Rankin scale scores at 3 months (odds ratio, 1.58 [95% CI, 1.10–2.27]; P = 0.013). In control patients, there was no significant correlation (odds ratio, 1.17 [95% CI, 0.87–1.55]; P = 0.298). Six of 7 thrombectomy patients with a large baseline infarct (ASPECTS <6) had a pediatric modified Rankin scale score of 0 to 2 at final follow‐up. Conclusion Baseline ASPECTS was significantly associated with clinical outcome in pediatric patients with large‐vessel occlusion stroke who received mechanical thrombectomy. Thrombectomy patients with low ASPECTS demonstrated favorable long‐term outcomes, suggesting ASPECTS alone should not be used to exclude pediatric patients from receiving thrombectomy.