States are double scheduling algebra classes; using calculators and virtual manipulative-like algebra tiles; and applying interventions such as Response to Interventions, needs assessments, and various computer graphing technology such as Demos. However, during the school year 2018-2019, 12.9 percent of a state public school students failed to meet passing score requirements on the state algebra test and were at risk of not graduating. The purpose of this research was to examine school principal perceptions and instructional leadership practices supporting mathematics teachers to help students to improve their proficiency in Algebra I. A basic qualitative research design, grounded in instructional leadership practices and Hitt and Tucker's unified framework, was used to examine principals' application of instructional leadership practices. The research question of this study addressed principals at the high schools under study regarding instructional leadership practices supporting mathematics teachers to help students to improve their proficiency in Algebra I. Data collected from semistructured interviews with two participants was analyzed through coding and thematic analysis. Findings from the study were that high school principals applied instructional leadership practices through (a) building strong relationships, (b) facilitating high-quality learning experiences, and (c) building professional capacity. Recommendations for best principal instructional leadership practices in support of teachers' daily instructional practices to help students improve proficiency in Algebra I could be made based on data collected from this study. Findings may contribute to positive social change by aiding principals in applying instructional leadership practices to help teachers assist students with Algebra I proficiency and increasing algebra state scores. [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.]