Objective: To evaluate the effects of a nutrition education programme conducted during health education lessons on students' adherence to the Mediterranean Diet (MD) and their body mass index (BMI). Design: Quasi-experimental pre-test/post-test research design: two study conditions (intervention and control groups). Setting: Two urban schools, the 11th and 21st primary schools in Limassol, Cyprus. Method: Two hundred and thirty-five fifth- and sixth-grade students participated in the programme. One hundred and fifteen were in the intervention group school (the 11th primary school), and 120 were in the control group school (the 21st primary school). Students in the intervention school participated in nine 80-minute lessons during the health education class. The curriculum focused on the MD and included cooking activities, food tasting and parental involvement. The primary outcomes were subsequent adherence to the MD, nutritional knowledge, self-efficacy physical activity and BMI. Results: Following the implementation of the intervention, the intervention group showed a significant increase in nutritional knowledge, self-efficacy and adherence to the MD (p < 0.001). The intervention group also had significantly higher nutritional knowledge and MD Quality Index scores than the control group (p < 0.001). However, no effect was observed on children's BMI (p > 0.05). Conclusion: The intervention successfully improved children's dietary habits in the intervention group by increasing adherence to the MD, but it did not affect their BMI. The results show some promise for addressing poor nutrition through education.