This article provides a description of how a beginning special education teacher in an inclusion classroom used pre-assessment, self-assessment, and on-going assessment to implement the principles of differentiated instruction to become more responsive to her students' needs in a systematic way. This article describes a case study of one beginning teacher's use of differentiated instruction. First, a discussion of the usefulness of differentiated instruction in increasing the likelihood of success for children with disabilities is provided. Next, qualitative data supported the implementation of the differentiated instruction process to help the teacher realize how she could positively impact students' learning using Tomlinson's (2000) categories of content, product, process, and learning environments. Finally, recommendations are provided for how to engage teachers to implement differentiated instruction as a data-based iterative process of using evidence-based practices to meet the needs of all children in an inclusion classroom. (Contains 2 tables.)