Across the United States, K-12 schools are challenged by rapid growth in the percentage of students of color, culturally and linguistically diverse students, and students from low-income families. A failing practice in the educational system has been to teach these diverse students as if they were the same. This quantitative study examined the relationship between professional development and teachers' attitudes toward implementing differentiated instruction in response to student readiness, interests and learning profiles to improve student achievement. The theoretical underpinnings of this study suggest that students who are taught in ways that are responsive to their readiness levels, interests and learning profiles are more successful. Research findings further suggest that (1) matching tasks to a student's level of development improves learning, and (2) there is a relationship between student achievement and a teacher's ability to diagnose where students are and eventually prescribe appropriate tasks. Personal interest used in learning enhances motivation, achievement, and productivity. The benefits of differentiation are promising but additional studies must document which elements of differentiation benefit certain students, to what extent and under what conditions. This study informs school district administrators of the types of professional development and coaching teachers need to carry out differentiated instruction. [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.]