The purpose of this quantitative pre-experimental research was to examine if, or to what extent, post-test scores were higher than pre-test scores in math and reading among elementary students in the Pacific Northwestern United States after participation in a mindfulness-based intervention (MBI). The Collaborative for Academic, Social, and Emotional Learning (CASEL) Framework served as the theoretical foundation for understanding MBIs as social-emotional learning (SEL), as they relate to academic achievement. This study addressed two research questions. First, were post-test scores statistically higher than pre-test scores in math among elementary students after participation in a mindfulness-based intervention (MBI)? Second, were post-test scores statistically higher than pre-test scores in reading among elementary students after participation in a mindfulness-based intervention (MBI)? Five classrooms with third and fourth grade students from a single elementary school participated in this study. The participants took part in a daily MBI at the start of the school day and after recess over the course of approximately eight weeks. The sample included 88 students' math pre-test and post-test scores and 81 students' reading pre-test and post-test scores. Quantitative data from the Star Math and Star Reading progress monitoring assessments, the pre-tests and post-tests in this study, were analyzed using paired-samples t-tests. Results revealed that post-test scores were statistically higher than pre-test scores in math (p < 0.001) and in reading (p = 0.004) among elementary students after participation in an MBI. The conclusions may be beneficial to other researchers and educational professionals. Keywords: Academic achievement, CASEL Framework, math, mindfulness-based intervention (MBI), reading, social-emotional learning (SEL). [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.bibliotheek.ehb.be/en-US/products/dissertations/individuals.shtml.]