Using the data from the All-Japan Utstein Registry, this study evaluates the neurologically favourable patient outcomes and associated factors of out-of-hospital cardiac arrest (OHCA) with Japanese schoolchildren as witnesses. Methods: We analysed 1,068 school-age children (6-18 years old) who underwent OHCA from 2011 to 2016. Among the 1,068 cases, 179 were witnessed by schoolchildren and 889 were witnessed by other bystanders. Propensity score-matched and logistic regression analyses were used to evaluate the outcomes and associated factors. Results: The crude neurologically favourable outcome in the schoolchildren-witnessed group was considerably higher than that in the other-bystander-witnessed group (19.6% versus 12.3%; P < 0.010). However, the difference was not significant in the propensity score-matched analysis (19.6% versus 21.8%; P = 0.602). The multivariable logistic regression analyses of school-age OHCA with schoolchildren as witnesses demonstrated that bystander cardiopulmonary resuscitation (CPR) provision (odds ratio [OR] 4.12, 95% confidence interval [CI] 1.44-11.75), shockable initial rhythm (OR 3.39, 95% CI 1.43-8.04), and defibrillation (OR 4.58, 95% CI 1.65-12.71) provided by any bystander were positively associated with favourable outcomes. By contrast, dispatcher-assisted CPR provision (OR 0.28, 95% CI 0.11-0.70), exogenous cause (OR 0.16, 95% CI 0.03-0.86), adrenaline administration (0.25; 95% CI 0.07-0.92), and prolonged response time (OR 0.86; 95% CI 0.75-0.98) were negatively associated with favourable outcomes. Conclusions: Patient outcomes did not differ significantly between schoolchildren-and other-bystander-witnessed cases of schoolage OHCA. Although schoolchildren as witnesses might not be inferior to other bystanders in school-age OHCA, further studies are needed to examine the effect of bystander CPR by schoolchildren and basic life support education in schools.