Multiple studies of recent decades have established close relationships between spatial skills and STEM achievement. Interventions have been effective in providing evidence of malleability of spatial skills and positive impact, yet the inclusion of spatial skills in curricula and policy lags. To date, only limited research has examined the impact of intervention with our youngest students, and the inclusion of motor skills has only rarely been a focus of studies of the spatial skills/STEM achievement relationship. Furthermore, female achievement in STEM still presents challenges for American society despite a plethora of initiatives to engage female students in STEM opportunities. The study investigated spatial skills as influencing factors of STEM achievement of 177 students of grades 3 through 6 enrolled in a religiously affiliated school in Louisiana during the 2014-2021 academic years. The study indicated that the established MNRI intervention had a statistical and practical impact on mathematics achievement for grades 3 and 4 sub-group participants and for established intervention sub-groups having one and two years of intervention at the two years post intervention testing interval. Statistical results offered insight into the potential decrease in gender differences in math achievement. When considering the importance of cultivating a more robust STEM workforce for the benefit of American society, the findings support the argument for further examining elementary interventions such as MNRI that may ameliorate gender disparities and address foundational deficiencies that support the development of spatial skills in our youngest students, a hinge point of STEM achievement. By illuminating the impact of the MNRI intervention, the findings of the study will help to inform decisions for continuation or expansion of the intervention or similar efforts. [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.]