Aim: The aim was to investigate the perceived self-esteem and self-estimated physical activity levels in connection with the Aktivitet Förebygger project for third graders in a school based in Sweden, as well as to investigate whether there were any gender differences in the students perceived self-esteem.  Method: This study has a parallel convergent mixed method design including 10 qualitative semi structured interviews and a quantitative survey which had 60 respondents. Qualitative data was transcribed, coded and categorized through a thematic analysis to identify patterns. Quantitative data was analyzed through a descriptive analysis where means and standard deviations were calculated alongside a t-test to compare results before and after respective project.  Result: The study showed that participation within Aktivitet Förebygger had a positive effect on students domain specific self-esteem. But the effect on children's global self-esteem was limited. No significant differences regarding gender differences related to self-esteem were found.  Conclusion: The findings of this study emphasizes that Aktivitet Förebygger has had a positive effect on children's self-esteem but further research is necessary to examine how great the impact is.