The study assesses the effects of long-term movement integration intervention in academic lessons of primary education (6th grade) on physical activity levels and sedentary behaviour, executive functions, academic achievement and on-task behaviour. To achieve it, a cluster randomized controlled trial design will be adopted, where schools will be the clusters.

The evidence shows that over 50% of Spanish children do not achieve the PA recommendations established by the WHO, and are therefore at higher risk of both short-term (e.g., overweight and obesity) and long-term health consequences (chronic illness in adolescence and adulthood). This is an alarming social and public health challenge in Spain and across Europe and effective solutions are needed.

Therefore, in this cluster randomized controlled trial, it will be tested if a long-term movement integration intervention in academic lessons (MovIn-Lessons) in primary education (specifically 6th grade) can increase the physical activity levels of children and reduce the sedentary behaviour at school-time. Additionally, it will be tested if this intervention can improve the executive functions, academic achievement and on-task behaviour.

Movement integration is defined as infusing physical activity, at any level of intensity, within general education classrooms during school time. Specifically, MovIn-Lessons intervention will consist of infusing physical activity in math, English and natural sciences lessons for all children attending the intervention schools. This will be achieved by carrying out learning activities in an active way.

Participants include children that are studying the 6th grade in primary education schools. Due to the cluster-randomized controlled trial design, the schools will be the clusters, and the design will have a restriction. The restriction is each cluster (school) that participates has to be from different towns or cities, even if schools are allocated to the same arm (intervention or control group). The aim of this restriction is to preserve construct validity by avoiding the fact that children from different schools in the same town or city could communicate with each other.

The recruitment will be following this procedure: all Catalan schools in the provinces of Barcelona and Girona will receive an invitation to participate in the study. Schools that are interested in taking part and meet the inclusion criteria will be eligible to participate. Schools will be randomly allocated to intervention or control group with matching. The matching criteria will be schools' characteristics (public or private, geographic location, sociodemographic profile and number of sixth grade classrooms) and teachers' characteristics (experience, confidence and pedagogical models used). Additionally, an allocation concealment mechanism will be used to prevent clusters' selection bias. All eligible participants will complete baseline assessments and follow-up evaluations conducted in the middle of the intervention (after three months), and one-week post-intervention.

Inclusion Criteria:

• children in sixth grade of primary education

Exclusion Criteria:

• children who require special educational needs and it is not following the whole-group classes

Only an allocation concealment mechanism will be used to prevent clusters' selection bias