This case study describes a teacher's development of and creativity in manipulating physical models in an astronomy course for in-service science teachers of K-8. Specifically, she organized a data table from several charts of numbers, constructed a moon-ball model in addition to a 2-D model, and created a hula hoop model as a concrete realization of her mental model. Examination of the transformation and construction processes revealed how she revised existing models and added new elements. These reconstruction experiences afforded her with a higher level of comprehension and self-awareness of her mental models. Three of the teacher's actions contributed to her increased understanding and deployment of the models: she enhanced her autonomy by changing the given models and solving problems she was interested in; she communicated with her partners and shared her knowledge by materializing her models; and she constructed new models on the basis of her experience. This case study shows that the transformation process, especially a cascade of small steps with the emergence of a more dramatic departure, is a key to generating scientific knowledge. (Contains 6 figures.)