Purpose: The purpose of this study was twofold: (a) Identify and describe principal and teacher perceptions of the effectiveness of Kotter's strategies used to facilitate change in instructional delivery to improve student success in Algebra 1; (b) identify and describe which strategies used by principals and teachers were perceived as most important in supporting change and overcoming barriers to change teacher instructional delivery to improve student success in Algebra 1. Methodology: The study was a descriptive, mixed-methods design. All schools in Fresno County where Algebra 1 is taught to eighth-grade students were identified. Of the 31 school districts in the county, 19 agreed to participate. Twenty-one principals and 20 teachers agreed to participate in a quantitative, electronic survey. Six principals and 6 teachers agreed to participate in a follow-up qualitative telephone interview. Findings: Principals leading change in teacher instructional delivery benefitted from using Kotter's strategies. Principals and teachers felt the most effective strategies were empowering broad-based action and communicating a vision and strategy. Few principals or teachers blamed lack of student success in Algebra 1 on student cognitive development. Principals and teachers reported that students were more successful in Algebra 1 when teachers employed explicit instruction and student engagement strategies. Principals and teachers found that the barriers of time and the ability to make new strategies routine were best overcome when provided the opportunity to collaborate, review student data, and consider best practices with peers through professional learning communities. Conclusions: Principals and teachers benefit when principals use Kotter's strategies for leading teachers in changing instructional delivery. Providing explicit instruction is an essential element in student success in Algebra 1. Instructional leaders providing ongoing training, coaching, feedback, and opportunities for peer collaboration through professional learning communities empower teachers with the necessary skills to overcome perceived barriers. Recommendations: Principals participate in training to better understand leading change in school settings. It is also recommended principals develop a clear vision for professional development to increase teacher skills in providing explicit instruction. Further research needs to be done in a larger number of schools correlating student success with instructional delivery. [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.]