Diet and Physical Activity (PA) habits are formed at a young age, and unhealthy habits can lead to childhood obesity and lifelong health problems. Schools are globally recognised as having access to children across all socio-economic backgrounds and to play an important role in influencing healthy habits. This Dutch experimental longitudinal study looks at the impact Primary schools can have on the health of their students by implementing a dedicated Nutrition and PA Program called ‘Healthy Primary Schools for the Future (HPSF), modelled on an American initiative, piloted in 4 schools and 2 control schools. The study tests whether a fully implemented program (focused on Nutrition and PA - including free lunches & daily PA sessions) or a partial program (focused only on PA sessions) influences healthy change in children’s behaviours versus control schools (no program). The data from 1676 children aged 4-12 yrs was used and the study took place over 3 yrs (2015-2017) with a commitment to continue till 2019 where follow-up data could be obtained. The data was collected once a year using parental and child questionnaires. Additional movement data was obtained from accelerometers the children wore for 7 days during each annual measurement week. The results at year 3 show that a combined nutrition and PA program had greatest benefits on improving diet (variety of foods eaten), and reducing unhealthy snacking, and increasing PA. Neither the partial program or control schools displayed positive changes. The researchers reflect that the full program allowed greater involvement from all parties involved (schools, parents, children’s, educational and health partners) which led to changes becoming an integral part of the school routine. Focusing on nutrition and PA together seemed to encourage complementary behavioural changes compared to focusing only on PA.