Executive functions (EF) can be promoted by classroom interventions. Our study investigated whether (a) an intervention conducted by teachers improves EF in children; (b) there are effects on behaviour and academic achievement; and (c) there are stable benefits in a one-year follow-up. Fifty-eight first-graders, divided into experimental (EG = 28) and control (CG = 30) groups, were assessed in EF, reading and arithmetic tests. Parents and teachers answered EF and behaviour functional scales. The intervention was conducted by teachers in the classroom context. EG children showed greater gains in EF and outperformed controls on reading and arithmetic measures. The EG maintained better performance in the one-year follow-up and showed transfer effect for behaviour measures. The EF intervention may be a useful tool for promoting improved adjustment and academic achievement.