The purpose of this study was to expand on existing parental socialization models of youth achievement motivation for engaging in physical activity. This study examined the extent to which youth affective reactions and expectancy-value beliefs mediated the relation between parental influence tactics and youth physical activity. More specifically, the direct and indirect effects of parents' positive, negative and sedentary-control tactics, the direct effect of parents' desire to change their child's physical activity, and the moderating role of the socio-emotional climate on the relation between parental influence tactics and child outcomes were investigated. Data were collected from 171 4th, 5th, 7th, 8th and 9th grade students and their parents. Pedometers were used to collect youth physical activity data and all participants completed questionnaires. Youth expectancy-value beliefs and negative affective reactions to parental influence tactics were both positively related to youth physical activity. Path analyses revealed that youth expectancy-value beliefs and negative affective reactions fully mediated the direct effects of positive and negative parental influence tactics on youth physical activity, respectively. Moreover, parents' desire to change their child's physical activity was negatively related to parent's use of positive influence tactics. Although several moderators were examined, none were statistically significant (lowest p >.05). The results suggest that additional explanatory power is gained by including a broader range of parental influence tactics and youth affective reactions in models of achievement motivation. The findings are in accord with prior recommendations made to parents with sedentary children.