Introduction: The development of fundamental movement skills (FMS) is essential to acquiring the necessary skills that allow children to be competent in several sports, games and dances. Competence is acquired from FMS skills through practice and experiences during childhood. However, evidence from previous studies showed low levels of FMS, given that 4.4% of the preschoolers were delayed in gross motor skills, and 8.8% were at risk of delay.

Aim: To evaluate the effects of a structured physical education (PE) program on preschoolers' FMS, implemented and delivered by PE teachers. Secondary aims are to evaluate the effects of the physical education program on (i) preschoolers' movement behaviors, (ii) physical fitness levels, and (iii) blood pressure.

Methods: Cluster randomized controlled trial study. Sample: 40 preschool children, aged 3 to 4 years old. Primary Outcomes are FMS, assessed with the Test of Gross Motor Development- Third Edition. Secondary outcomes are physical activity (PA), physical fitness, blood pressure and Body Mass Index (BMI).

Expected results: Participation in the PE program will likely have a positive effect on the development of FMS, potentially increasing PA levels and improving physical fitness. It is also expected that FMS show a consistent positive association with BMI and blood pressure levels. The results of this randomized controlled trial (RCT) have the potential to inform future guidelines for PE classes in Chilean preschoolers and strengthen the scientific knowledge on this type of intervention in this population.

Data from children and adolescents has shown that FMS have a significant association and reciprocal longitudinal relationship with PA. Strong evidence to supports a low-to-moderate positive association between FMS and moderate-to-vigorous and vigorous and vigorous PA in preschool-aged children. Conversely, when analyzing results within the 24-hour movement behaviors spectrum, there is evidence that preschoolers who spend more time in sedentary behavior have lower FMS' scores. Short sleep durations can adversely affect the development of FMS. Previous findings also show that proficient FMS may benefit children's physical fitness, specifically cardiorespiratory and musculoskeletal fitness.

FMS' development should begin in the early years; however, data shows that many preschoolers lack adequate FMS proficiency for their age. Additionally, some data show that the Covid-19 worldwide pandemic damaged preschoolers' FMS, together with the motor competence of children aged 6-9 years old, highlighting the need for tailored interventions. Indeed, FMS intervention programs effectively improve FMS, as well as other health-related behaviors and outcomes in preschoolers. Unfortunately, in Chile, many preschools and primary schools do not have structured PE programs, but rather recreation periods in which children participate in free play. However, it has been shown that young children spend only half of their free play time engaged in PA and that PE interventions are an effective mean for developing FMS in preschoolers, but only when implemented by specialized PE teachers. However, in Chile, it is not common to find PE teachers in preschoolers.

Therefore, this research's main aim is to evaluate the effects of a structured PE program on preschoolers' FMS implemented and delivered by PE teachers. The secondary aims are to evaluate the effects of the PE program on (i) preschoolers' movement behaviors, (ii) physical fitness levels, and (iii) blood pressure.

The hypothesis is that a structured physical education program positively modifies fundamental movement skills, movement behaviors, physical fitness levels, and blood pressure.

Inclusion Criteria:

• Preschool children, 3 to 4 years old

Exclusion Criteria:

• Diagnosed physical or mental impairments.