This paper reports on the evaluation of an 11-week curriculum created to foster seventh grade students' understanding of scientific modeling. In the curriculum, students engaged in model-oriented activities such as creating non-Newtonian computer microworlds to embody their conceptual models, evaluating their models with criteria, and reflecting on the nature of models. Various methods of assessing modeling are also discussed. The overall analysis suggests that students gained a significantly better understanding of the nature and utility of models without promoting similar gains in students' understanding of the process of creating and evaluating models. These results indicate that while modeling knowledge is difficult to obtain even from an extended model-focused curricula, progress can be made by further refining model-oriented curricula and assessments. (Contains 39 references and written modeling assessment results.) (DDR)