ObjectivesThe primary goal of this study was to investigate the influence of the Mindfulness Education Workbook, a 6-week mindfulness-based tool, on emotion regulation, inhibition, physical self-concept, resources, and connectedness to nature. Furthermore, we explored whether a difference in number of hours of mindfulness practice would affect the outcomes.MethodNinety-one children from a public elementary school (M age = 9.74 years, SD = 0.76) participated in the study and were divided into three groups according to their respective school classes. The intervention group was divided into two groups that varied by number of hours of mindfulness practice: (a) mindfulness-plus and (b) mindfulness. In addition to biweekly training, the mindfulness-plus group also repeated a daily exercise. The passive control group received the standard school day instruction. The five concepts of emotion regulation, inhibition, physical self-concept, resources, and connectedness to nature were measured before and after the mindfulness intervention.ResultsFor the measurement of emotion regulation, there was a significant effect in favor of the two mindfulness groups compared with the control group for the adaptive strategies in total as well as for their comprising emotions, anger, fear, and sadness, separately. Solely for the subscale mood elevation, the mindfulness-plus group showed significantly higher scores compared to the control group. Both mindfulness-plus and mindfulness groups varied from the control group on the measure of emotion regulation strategies, however not on the other four domains that were assessed (self-reports of resources, physical self-concept, and connectedness to nature as well as a mental task assessing inhibition). There was no evidence that the additional practice in the mindfulness-plus group significantly added to the intervention's effectiveness.ConclusionsThe Mindfulness Education Workbook is a promising tool for elementary schools. Follow-up studies may provide further insights into the various effects of offering mindfulness training in schools. Further research with objective markers may also allow individual aspects under the umbrella term mindfulness to be investigated in more detail.PreregistrationThis study was not preregistered.