The authors examined internal representations of conditional strategies for a situation of object conflict in 849 adolescents and young adults between the ages of 11 and 19 years. To examine participants' expectations of strategy use, the authors developed questionnaires that depicted a variety of contexts in which 2 people wanted an object that could not be shared. Results indicated that internal models produced a modulation of the probability of use of several potential strategies according to the levels of various factors. Overall, participants' expectations were consistent with existing empirical data, including developmental trends toward decreased aggressive behavior. Self-report data produced lower levels of expected aggressive behavior, with the divergence between self-reports and other reports larger when the contested object was more important for physical well-being. Results also indicated that internal models can be structured as conditional strategies, and when aggregated among many participants, internal models are accurate reflections of behavior. (Contains 1 table and 1 note.)