Objective Examine youths' perceptions of police legitimacy. Study one establishes age-graded trends in perceptions from childhood into adolescence. Study two tests whether a structured, in-school, non-enforcement-related program involving repeated prosocial exposure to police can improve youths' perceptions of police legitimacy. Methods In study one, a cross-sectional sample (N = 959) of youth ages 7 to 14 was used to assess age-graded perceptions of police legitimacy. In study two, a 4-school, randomized controlled trial was conducted in Compton, California (N = 499). Results Age-graded differences in police legitimacy perceptions vary by race, but generally begin declining during late childhood. The program significantly improved youths' perceptions of police legitimacy. Conclusion Racial differences in perceptions of police legitimacy can be traced to childhood, and perceptions of law enforcement appear to begin declining during childhood. Further, repeated exposure to law enforcement officials in a positive, non-enforcement capacity may improve youths' legitimacy perceptions.