The purpose of this study was to explore students' mathematical practices while working on modeling problems using 3 interactive computer simulations. Three fifth grade students' interactions with computer-based modeling simulation were examined to identify how children defined and prioritized and coordinated variables and parameters in dynamically simulated environments to focus their work on modeling activities. I traced what students noticed at the point of entry into each simulation, key factors they considered to determine, explain, and predict the potential changes in the results of a simulation with altered parameters. Results of the study showed that students benefited from exposure to simulations to gain a better perception of a problem with interacting variables. In particular, animated graphics of the simulations helped the participants to visualize the problem, learn about the effect of different variables on the outcomes of the task situations hence, effecting the participants' modeling process across activities. Interactions with simulations increased the participants' ability to manage the scope of obstacles they had encountered when working on modeling tasks prior by serving as a visualization tool, a discovery tool, a virtual lab, a hypothesis tester, a solution tracker, and a calculator. [The dissertation citations contained here are published with the permission of ProQuest LLC. Further reproduction is prohibited without permission. Copies of dissertations may be obtained by Telephone (800) 1-800-521-0600. Web page: http://www.proquest.com/en-US/products/dissertations/individuals.shtml.]