Background: It has been proved that bystander cardiopulmonary resuscitation (CPR) saves lives; however, which training method in CPR is most instructive and whether survival is affected by the training level of the bystander have not yet been fully described. Aim: To identify the factors that may affect 7th grade students’ acquisition of CPR skills during CPR training and their willingness to act, and to describe 30-day survival from outof- hospital cardiac arrest (OHCA) after bystander CPR and the actions performed by laymen versus off-duty medically educated personnel. Methods: Studies I–III investigate a CPR training intervention given to students in 7th grade during 2013–2014. The classes were randomized to the main intervention: the mobile phone application (app) or DVD-based training. Some of the classes were randomized to one or several additional interventions: a practical test with feedback, reflection, a web course, a visit from elite athletes and automated external defibrillator (AED) training. The students’ practical skills, willingness to act and knowledge of stroke symptoms, symptoms of acute myocardial infarction (AMI) and lifestyle factors were assessed directly after training and at 6 months using the Laerdal PC SkillReporting system (and entered into a modified version of the Cardiff test scoring sheet) and a questionnaire. The Cardiff test resulted in a total score of 12–48 points, and the questionnaire resulted in a total score of 0–7 points for stroke symptoms, 0–9 points for symptoms of AMI and 0– 6 points on lifestyle factors. Study IV is based on retrospective data from the national quality register, the Swedish registry of cardiopulmonary resuscitation, 2010-2014. Results: A total of 1339 students were included in the CPR training intervention. The DVD-based group was superior to the app-based group in CPR skills, with a total score of 35 (SD 4.o) vs 33 (SD 4.2) points directly after training (p<0.001) and 33 (SD 4.0) vs 31 (SD 4.2) points at six months (p<0.001). Of the additional interventions, the practical test with feedback had the greatest influence regarding practical skills: at six months the intervention group scored 32 (SD 3.9) points and the control group (CPR only) scored 30 (SD 4.0) points (p<0.001). Reflection, the web course, visits from elite athletes and AED training did not further increase the students’ acquisition of practical CPR skills. The students who completed the web course Help-Brain-Heart received a higher total score for theoretical knowledge in comparison with the control group, directly after training: stroke 3.8 (SD 1.8) vs 2.7 (SD 2.0) points (p<0.001); AMI 4.0 (SD 2.0) vs 2.5 (SD 2.0) points (p<0.001); lifestyle factors 5.4 (SD 1.2) vs 4.5 (SD 2.0) points p<0.001. Most of the students (77% at 6 months), regardless of the intervention applied, expressed that they would perform both chest compressions and ventilations in a cardiac arrest (CA) situation involving a relative. If a stranger had CA, a significantly lower proportion of students (32%; p<0.001) would perform both compressions and ventilations. In this case, however, many would perform compressions only. In most cases of bystander-witnessed OHCA, CPR was performed by laymen. Off-duty health care personnel bystanders initiated CPR within 1 minute vs 2 minutes for laymen (p<0.0001). Thirty-day survival was 14.7% among patients who received CPR from laymen and 17.2% (p=0.02) among patients who received bystander CPR from off-duty health care personnel. Conclusions: The DVD-based method was superior to the app-based method in terms of teaching practical CPR skills to 7th grade students. Of the additional interventions, a practical test with feedback was the most efficient intervention to increase learning outcome. The additional interventions, reflection, web course, visit from elite athletes and AED did not increase CPR skills further. However, the web course Help-Brain-Heart improved the students’ acquisition of theoretical knowledge regarding stroke, AMI and lifestyle factors. For OHCA, off-duty health care personnel bystanders initiated CPR earlier and 30-day survival was higher compared with laymen bystanders.