This study investigates the changeability of transport-related attitudes and mode choice of early adolescents. Data on attitudes and travel behavior were collected in Austria and Germany in two consecutive survey waves with an interval of one year. The approach is based on a before-after control group experiment with an intervention promoting active travel modes. Based on the Theory of Planned Behavior we used structural equation modeling analyzing effects of the intervention; the potential for behavioral changes was modelled as moderator variable between intention and behavior. Findings suggest that the intervention was effective in changing attitudes, perceived behavioral control (PBC) and intentions to use non-motorized travel modes more, and car less. Difference models show that changes of attitude, subjective norm, and PBC accounted for 29% (car passenger) to 92% (walking) of the variance in changes in intention. The changes in intentions are however weak predictors of changes in reported behavior.