This study evaluates the 2008–2009 “Lose your Excuse” public service advertising (PSA) campaign on energy efficiency targeting 8- to 12-year-olds, intended to increase knowledge, foster proactive attitudes, and change energy usage behaviors. Baseline and two follow-up surveys were conducted with online samples representative of the national population of households with kids with online access. Almost half (47%) of the tweens recognized at least one ad from the campaign. Ad recognition was positively associated with knowledge, proactive attitudes, and energy-saving behavior. Propensity score analysis confirmed a small but measurable and statistically significant effect on energy-saving behavior. The discussion section compares these results to public health campaigns in terms of ghost awareness, reach, and effect size.