The present study examined whether both dis- positional mindfulness without mindfulness training and mindfulness resulting from longer-term mindfulness training are positively associated with pre-adolescents’ well-being, via enhanced executive functioning (EF) and emotion regu- lation. EF was assessed in a GoNoGo task via behavioral performance and event-related potentials. Study 1 (N = 62) investigated associations of dispositional mindfulness with- out mindfulness training with EF, well-being and emotion regulation; longitudinal Study 2 with an active control group compared the effects of long-term mindfulness training (N = 28) with a positive psychology intervention (N = 15). Dispositional mindfulness without training was associated with lower EF, unrelated to emotion regulation and the rela- tionship with well-being was mixed. Long-term mindfulness training was positively related to EF and well-being (reduced negative affect), but was uncorrelated with emotion regu- lation and mindfulness scores. Taken together, long-term mindfulness training was found to have mixed effects. Fur- ther research is required in this area.