title: Participation in extracurricular physical activity programs at middle schools.
authors.affiliation: Community Pediatrics at the University of California San Diego, USA.
authors.forename: Holly S
authors.initials: HS
authors.lastname: Powers
authors.forename: Terry L
authors.initials: TL
authors.lastname: Conway
authors.forename: Thomas L
authors.initials: TL
authors.lastname: McKenzie
authors.forename: James F
authors.initials: JF
authors.lastname: Sallis
authors.forename: Simon J
authors.initials: SJ
authors.lastname: Marshall
mesh_terms: D000293:Adolescent; D002140:California; D002648:Child; D005260:Female; D006801:Humans; D008297:Male; D010806:Physical Education and Training / Q000458:organization & administration / Q000706:statistics & numerical data*