Differentiated instruction (DI) is a curriculum framework that focuses on the individual student. Students achieve because teachers develop lessons to the students' readiness levels, interests, and learning styles. Students in early childhood through college have shown increased achievement when DI is implemented. The purpose of this quantitative, causal comparative study was to compare self-efficacy about DI and the frequency DI was implemented between first-year teachers and teachers with more than one-year of experience. The problem is teachers often do not implement DI in the classroom because it is perceived as too challenging. This study obtained information from 97 first through fifth grade teacher participants. The participants were randomly selected from 4 southwest Oklahoma elementary schools. A quantitative, causal-comparative research method was implemented to determine if there was a difference between teachers' self-efficacy about DI and the frequency teachers implement DI in their classrooms. The findings from the One-Way MANOVA statistical test revealed there was a significant difference of p < 0.05 between first year teachers and teachers with more than one year of experience for self-efficacy and frequency DI was implemented. By investigating whether first year teachers or teachers with more than one year of experience were more likely to implement DI, the field of education will gain a better understanding on how to improve either teacher preparation programs for first-year teachers or professional trainings/mentorships for teachers with more than one-year of experience. [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.]