Education of schoolchildren in cardiopulmonary resuscitation (CPR) is a strategic goal for improvement of bystander CPR in society. The primary objective was to analyse the impact of CPR training on the resuscitation knowledge and self-confidence of secondary schoolchildren. In addition, independent predictors of improved CPR knowledge and self-confidence were investigated. Randomised-interventional controlled study. Four secondary schools in Germany. Four hundred and twenty-four schoolchildren aged from 14 to 18 years were included into the study. Fifty-one percent were female, and 33% had an immigrant background. The intervention group received a 90-min CPR training session, whereas controls had no intervention. Levels of knowledge and self-confidence in initiating CPR were analysed by a study questionnaire before (t0), 90 min after (t1) and 6 months after training (t2). Based on the evaluation of study questionnaires, the primary endpoint was to determine the development of resuscitation knowledge and self-confidence in initiating cardiopulmonary resuscitation at survey time-points t0, t1 and t2. Schoolchildren in the intervention group (n=207) showed a significantly higher level of knowledge (P < 0.001) and self-confidence (P < 0.001) at t1 and t2 compared with controls (n=217). Age was a predictor for long-term self-confidence [odds ratio (OR), 1.20; 95% confidence interval (95% CI), 1.02 to 1.41; P = 0.032]. The long-term benefit in the level of knowledge and self-confidence were significantly higher in native compared with immigrant schoolchildren: (OR, 1.79; 95% CI, 1.14 to 2.82; P = 0.011) and (OR, 1.67; 95% CI, 1.07 to 2.60; P = 0.024), respectively. Guideline compliant (90 min) theoretical and practical CPR training improves the level of knowledge and self-confidence in 14 to 18-year-old schoolchildren. Older schoolchildren are more likely to have increased self-confidence with respect to initiating CPR. Schoolchildren with an immigrant background showed a significantly lower increase in their level of knowledge and self-confidence compared with native children. Adaptation and simplification of teaching materials and further research on educational methods for CPR are urgently needed to enable a sustainable approach to teaching CPR, which also produces a long-lasting effect in the entire population.