This article shares the first-hand experiences of the CDC's VERB team in planning, executing, and evaluating a campaign that used social marketing principles, which involved paid media advertising, promotions, and national and community partnerships to increase physical activity among children aged 9-13 years (tweens). VERB staff gained valuable experience in applying commercial marketing techniques to a public health issue. This article describes how marketing, partnership, and evaluation activities were implemented to reach a tween audience. In doing so, fundamental differences in marketing between public health and the private sector were revealed.