Too many students are entering post-secondary education lacking foundational mathematics skills that are critical to performance on placement examinations. As a result, students are forced to take remedial courses that are often non-credit bearing and hinder their progress toward graduation. Research suggests that a lack of number sense may contribute to poor performance on standardized assessments. Number sense consists of multiple skills and concepts embedded within a concrete understanding of how numbers are represented. One concept featured in number sense is computational estimation, an interaction of mental computation, number concepts, and technical arithmetic skills which is performed quickly (without any recording tools) and which results in answers that are reasonably close to a correctly computed result. This experimental study measured the impact of an intervention featuring supplemental activities in computational estimation delivered in game format. Students in tenth grade solved real-life mathematics questions independently and collaboratively, without any recording tools, with the goal of forming reasonable estimates. Over six weeks, students earned points for answers that fell within an appropriate range. Results of this study suggest that students without disabilities significantly improved their performance on standardized assessment questions featuring rounding, but did not outperform control groups in overall performance on questions encouraging the use of computational estimation. Students with disabilities did not demonstrate improved performance in any areas, suggesting the length of the study may have been too short for students who require more time to grasp new concepts and skills. [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://bibliotheek.ehb.be:2222/en-US/products/dissertations/individuals.shtml.]