Digital games are widely popular and interest has increased for their use in education. Digital games are thought to be powerful instructional tools because they promote active learning and feedback, provide meaningful contexts to situate knowledge, create engagement and intrinsic motivation, and have the ability individualize instruction. However, claims about the potential benefits of digital games in education have outpaced quality empirical research on their effectiveness in K-12 settings. The purpose of this study was to investigate the effectiveness of a mathematics digital game, Ko's Journey, on seventh grade students' mathematics achievement as defined by a researcher-constructed test aligned with the Common Core Mathematics Standards (National Governors Association Center for Best Practices, Council of Chief State School Officers, 2010) and measured on a Rasch (1960) unidimensional equal-interval scale. This research was conducted using secondary data from a pretest-posttest control group design study with a total of 371 seventh grade students from 10 classrooms. Classroom teachers randomly assigned their classroom sections to play the mathematics digital game or served as a wait-listed control group and continued using the typical mathematics curriculum. Hierarchical linear modeling (HLM) and Rasch differential item functioning were used to determine the effect of the intervention on student's mathematics achievement. Hierarchical linear modeling analyses, using person ability logit estimates derived from the Rasch scaling, concluded that the Ko's Journey intervention did not have a significant effect on posttest scores. The HLM analyses revealed a significant positive relationship between the students' individual pretest and posttest scores and the classroom average pretest and posttest scores. Using the Rasch differential item functioning, six assessment items were significantly less difficult for the experimental group compared to the control group; this suggested that the intervention was successful in teaching the mathematics targeted by the items. Technological problems experienced in the classrooms and differential implementation of the game among teachers confounded an accurate estimate of the efficacy of the digital game to improve academic achievement. [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.]