Introduction Numerous preventive programmes have emerged, and need to be investigated to determine their effects on the normal population. Earlier studies have shown a decrease in depressive symptoms, positive effects on children’s disruptive behaviour problems, and an improvement in parental competence. About a fifth of the parents in previous studies had problem-oriented (targeted) reasons for enrolment, whereas the rest of the parents had general (universal) reasons. The results of those studies suggest that the programmes are cost effective in terms of Quality-Adjusted Life Years. Aim Four sub-studies were performed, and their aims were to investigate the effect of parental training programmes (PTPs) in a naturalistic setting on parents’ mental health in the general population, to investigate how PTPs affect parents’ sense of parental competence, to investigate how PTPs affect parental stress and analyse the parents open questions about the PTPs, and to investigate the feasibility and to measure the effect on depression, anxiety, and social problems of two preventive school programmes for pupils in grade 7. Method In a longitudinal quantitative study in a real-world setting, 279 parents from the general population in northern Sweden participated in five PTPs. A comparison group of 702 parents without intervention was included. Simultaneously, a community sample of 59 pupils in grade 7 participated in two preventive school programmes. Both studies were conducted from 2010 to 2013. Parents were assigned to professionally supported interventions that included 5-10 two-hour sessions. Respondents filled in a web-based questionnaire with the General Health Questionnaire (GHQ), the Parents Sense of Competence (PSOC) for parents who had children aged 0-17 years, and the Swedish Parenthood Stress Questionnaire (SPSQ) for parents who had children aged 0-10 years. The intervention groups’ results were compared to comparison group of 702 parents from northern Sweden that had not participated in any parental training programme. In the school study, one of the preventive programmes was an ongoing programme called “Life-Skills”, and the other was an implemented Canadian programme called “Choosing Healthy Actions and Thoughts” (CHAT). The pupils completed a test battery including the Sense of Coherence (SOC), the Children’s Depression Inventory (CDI), and the Youth Self-Report (YSR) instruments. Follow up of the parental programme study was done six months after the post-intervention measure, and follow up of the school study was at one year. Results The improvements in GHQ were statistically significant for the mean of the 279 parents in the intervention group compared to the mean of a comparison group of the 702 parents who did not receive any intervention. This suggests that evidence-based PTPs enhance parental well-being even for parents without problems. The intervention group showed a statistically significant improvement in parental competence compared to the comparison group over time. The intervention itself had a significant effect on parental satisfaction, but the efficacy effect was not sustained when taking into account potential confounders. In the SPSQ, the intervention group was smaller due to the fact that the instrument was not validated for children over the age of 10 and one of the parental training groups was only for parents of teenagers. A reduction of stress in the sub-scale of health problems was detected, but no other subscale showed the intervention to have a significant effect when controlling for confounding variables. In the school study, both programmes had good feasibility according to the stake- holders and had several positive mental health outcomes over time. Compared to Life-Skills, CHAT had more significant positive effects on reducing anxious/depressive symptoms and girls experienced significant positive effects on reduced anxious/depressive behaviour, while boys reduced their aggressive behaviours. Conclusions Earlier studies indicate that PTPs enhance perceived parental competence among referred parents. The present study shows that PTPs applied in the general population might also enhance perceived parental benefits such as improved health and satisfaction, suggesting that PTPs can be an important preventive strategy to enhance parenthood. The results suggest that parents who feel a need to increase their parenting competence might participate in PTPs based on lower scores than the comparison control group both before and after the intervention. The school-based programme shows that schools may be a suitable arena for preventive programmes because there was a significant short-term improvement in depression symptoms. Further studies need to explore how parents’ participation in PTPs affects children’s mental health in the general population in quantitative longitudinal studies in real-word settings. There is also a need for bigger studies and RCTs on school preventions and on how children’s health develops naturally in the population.