Educational software can increase cognitive load and reduce learning in the K-12 classroom. The purpose of this quantitative quasi-experimental study was to compare the pretest/posttest changes in critical thinking skills and cognitive load in fourth-grade students after using multimedia software based on whether the design of the software product incorporated multimedia design principles. The Cognitive Theory of Multimedia Learning and Cognitive Load Theory supported the underpinning of this study. A mixed-model analysis of variance was conducted to determine whether significant differences existed in cognitive load pretest/posttest assessment between an experimental and control group. The experimental group consisted of 32 students and 30 students in the control group. The California Critical Thinking Skill Test and Paas and Van Merrienboer subjective rating scale test addressed the research questions by measuring students' pretest/posttest changes in critical thinking and cognitive load. The study showed no significant difference in the experimental and control pretest inference scores. The control group scored higher than the experimental group, however, both showed learning gains on pretest/posttest scores. The implications derived from these results were that students exerted less mental effort on the California Critical Skill posttest than on the pretest. Future research using a combination of multimedia principles relevant to individualized or personalized principle would be relevant in today's online learning environment. Also, further studies incorporating the five categories of the critical reading skills domain were recommended. [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.]