Strong knowledge of foundational mathematics concepts is essential for success in high school mathematics courses, yet only one-third of middle school students in Hawai'i demonstrated proficiency in grade-level mathematics in 2019. Despite this problem, there are only a few studies investigating interventions aimed at addressing gaps in students' knowledge, especially at the high school level. This case study investigated instructional intervention tools designed to help high school students who were struggling in mathematics strengthen their knowledge of and skill in foundational mathematics content. The two instructional intervention tools, a double dose program and conceptual mathematics games, developed by the Curriculum Research & Development Group (CRDG) at the University of Hawai'i at Manoa, were implemented in select mathematics classrooms at a high school in Hawai'i. Scores on progress monitoring assessments were used to determine student growth. While the primary focus of the study was to investigate the effects of the intervention tools on assessment scores for struggling learners, effects on the assessment scores for non-struggling learners were also analyzed. The findings showed that the use of games had a positive effect on scores for struggling learners and could be a promising tool for non-struggling learners as well. The double dose program did not show as strong positive results on assessment scores for either the struggling or non-struggling students. Implications for a future study are to observe and analyze the conditions of the supplementary course to investigate the efficacy of the program. [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.]