The present study presents the first attempt at investigating long-term mindfulness training in pre-adolescence, adopting an integrative neurodevelopmental approach. Pupils with an established mindfulness practice (n=33) were compared with mindfulness-inexperienced pupils (n=20) on dispositional mindfulness, executive functioning (EF), emotion regulation, and well-being. We also investigated whether increased well-being in mindfulness-experienced pre-adolescents would be mediated by EF and emotion regulation. Moderating influences of the amount and enjoyment of mindfulness training were considered as well. Self-report questionnaires measured dispositional mindfulness and well-being. Parents assessed their child's emotion-regulation using the Emotion Regulation Checklist (ERC). Performance in a Continuous Performance Task and simultaneously recorded event-related potentials (ERPs)--Cue-P3, CNV, Nogo-N2, Nogo-P3--indexed EF. Interestingly, the two groups of pupils did not differ in their dispositional mindfulness. ERP findings revealed that the mindfulness-experienced group demonstrated superior EF in terms of response inhibition, but inferior EF in terms of cue processing. Although the ERC negativity/lability subscale revealed an advantage for the mindfulness-experienced group, no group differences were observed for the ERC emotion regulation subscale or well-being. Mediation analysis results did not support the assumption that mindfulness training leads to increased well-being via improvements in EF and emotion regulation. While outcomes were not moderated by amount of mindfulness practice, enjoying mindfulness was negatively associated with indicators of well-being and EF.