With the increased interest in school-based mindfulness interventions, there have been repeated calls to investigate neurodevelopmental markers of change. This non-randomised study of 16–18 year olds with wait-list control group examined possible enhancements to brain indexes of attention processing after school-based mindfulness training using event-related potentials (ERPs) (N=47 for self-report; N=40 for ERPs). Results showed significantly more negative N2 amplitudes after training, in response to irrelevant frequent stimuli and colour-deviant non-target oddball stimuli in a visual oddball paradigm. Improvements in negative thought controllability were associated with more negative N2 amplitudes post-training across groups, and mindfulness training was associated with reductions in students' hypercritical self-beliefs. There were no group differences on task performance, but regression analysis indicated that programme satisfaction explained 16% of the variance in improved target accuracy. Together these results suggest that a school-based mindfulness curriculum can enhance older adolescents' task-relevant inhibitory control of attention and perceived mental competency.