The intentional integration of movement in elementary school classrooms—including both brief instructional breaks for
physical activity, or the integration of physical activity with lessons—can benefit children’s physical health and education
outcomes. Teachers are key implementation agents, but despite movement integration (MI) being considered an educational best
practice, many classroom teachers do not regularly use it. The aim of this study was to obtain updated nationally-representative
prevalence estimates in US public elementary schools, regarding four key outcomes pertaining to teachers’ implementation of physical
activity: 1) school adoption of physically active lessons (PALs); 2) school adoption of physical activity breaks (PABs); 3) penetration
rate to the classroom, defined as ≥50% of teachers using PABs; and 4) dose of PABs of at least 50 minutes per week. I examined
variations in outcomes by school demographic characteristics, and hypothesized implementation facilitators (administrative support,
financial resources, and presence of a wellness champion at the school). Surveys were distributed to a nationally-representative
sample of 1010 public elementary schools in the US; responses were obtained from 559 (55.3%). In 2019–20, the weighted prevalence
of schools having adopted PALs was 77.9% (95% CI = 74.3% to 81.4%), and PAB adoption was nearly universal at 91.5% (95% CI = 88.9%
to 94.2%). Few demographic differences emerged, although PAL adoption was less prevalent at the highest-poverty schools (74.01%)
and medium-poverty schools (77.0%) as compared to schools with the lowest student poverty levels (87.1%; p < .01). Across all
four outcomes, associations emerged with implementation facilitators in multivariable logistic regression models. The prevalence
of PAL adoption, PAB adoption, and dose of PABs were all significantly higher at schools where administrative encouragement
occurred more frequently. For example, at schools where the administrator provided encouragement often, 97.8% had adopted PABs,
versus 78.2% of schools where encouragement happened never or rarely (p < .001). Financial support was associated with
implementation outcomes, including higher PAL adoption, PAB penetration, and PAB dose. Presence of a champion was associated
with higher prevalence of PAL adoption. School leaders can play a crucial role in supporting their teachers’ use of MI
within the classroom, including the provision of financial resources, encouragement, and supporting champions. Effective
school leadership practices have the potential to positively impact health and education outcomes for children at a large-scale population level.