The ability to delay gratification at a young age is a predictor of psychological, cognitive, health, and academic later-life outcomes. This study aimed to extend earlier research and explore whether a metacognitive intervention, Wells' (1990) Attention Training Technique (ATT), could improve young children's ability to delay gratification compared to an active-control (Progressive Muscle Relaxation: PMR), and no-intervention group. One hundred and one children aged 5–6 years old were recruited from schools. Classes of children were randomly allocated to receive the ATT, PMR or no-intervention and tested at pre- and post-intervention on measures of delay of gratification (the Marshmallow Test) and verbal inhibition (Day/Night Task). Results showed that, even when covariates were controlled for, following ATT, children delayed gratification significantly longer than after PMR or no-intervention. ATT also improved verbal inhibition compared with the no-intervention group, whilst PMR did not. The results add to earlier findings; ATT appears to provide a simple and effective way of improving young children's ability to delay gratification which has previously been shown to predict positive outcomes in later-life.