Objectives: Tobacco power walls display hundreds of tobacco products and are known to be a key part of the impact of point-of-sale tobacco advertising on risk for smoking in adolescents. The current study examined factors that are hypothesized to mediate the effect of tobacco power wall exposure on adolescents’ susceptibility for smoking in the future. Method: Participants (N = 148) aged 11–17 years were invited to shop in the RAND StoreLab, a life-sized replica of a convenience store. They were randomized to 1 of 2 conditions: one in which the power wall was located in its typical position behind the cashier and the other in which it was hidden behind an opaque wall. Participants shopped in the RAND StoreLab and then completed measures of susceptibility for smoking in the future, perceived smoking norms, and perceived accessibility of cigarettes. Participants’ movements in the store were electronically tracked. Results: Having the tobacco power wall behind the cashier increased adolescents’ susceptibility for smoking in the future by 14.3% (total effect) compared with when the power wall was hidden (p = .01), and 14% of this effect was mediated by participants’ perceived smoking norms. Time spent in front of the cashier and perceived accessibility of cigarettes did not play a role in the association between study condition and susceptibility for smoking in the future. Conclusions: The tobacco power wall increases adolescents’ smoking risk, and this effect is partly explained by the effect of the power wall on adolescents’ perceptions of how normative smoking is.