Advocacy can create a social paradigm shift surrounding responsibility for obesity prevention. Youth advocacy for obesity prevention is a promising intervention with potential for political, environmental, social, and individual changes, but has not been studied in a systematic, theory-driven way. Youth advocacy training groups were recruited for the present study. Groups chose community audits of modifiable health environment factors (parks, fast food outlets, school, stores, outdoor advertising). Youth (baseline n=136, matched pre-post pairs n=92) and adult group leaders (baseline n=47, follow-up n=45) completed surveys to assess advocacy experiences. Aim 1 : Create advocacy readiness and receptivity subscales using confirmatory factor analysis (CFA) and describe the psychometric properties of the four surveys to evaluate youth advocacy programs. Aim 2 : Assess youth changes on behavioral/attitudinal subscales pre- and post-advocacy, using paired t-tests. Aim 3 : Create an advocacy readiness/receptivity index and evaluate roles of group, youth, and leadership factors on readiness/receptivity using generalized linear mixed models (GLMM). Aim 4 : Conduct a preliminary analysis of advocacy success based on adult leadership variables and group-level processes using GLMM. Youth came from 21 groups, ranged in age from 9-22, and 2/3 were female. Aim 1 : The proposed factor structure held for most youth subscales. Aim 2 : Two of the six attitudes/beliefs subscale scores, and four of the five knowledge/skills subscale scores increased significantly. Aim 3 : GLMM indicated that four of the youth attitude/behavior subscales were significantly positively associated with advocacy readiness/receptivity. Aim 4 : The only significant association was adults' prior experience with nutrition/physical activity. These analyses represent the first theory-driven, systematic study of measures and outcomes for youth advocacy for obesity prevention. The proposed factor structure was upheld or modified, and the resulting scales can be used in future studies. Significant improvements on six youth subscales indicated youth involvement in advocacy led to multiple positive psychosocial and knowledge-based changes. There were methodological limitations: multivariate analyses require larger sample sizes, so future studies should confirm these findings. Positive youth changes, adult leader experiences, and several successful advocacy projects point to an important role for well-designed and controlled future advocacy studies.