This study was an investigation of staff development programs designed to provide teachers with strategies through which all learners, including gifted, minority, and limited-English proficient students, can be appropriately served in a middle school environment sensitive to diverse learner academic needs. Participants in the study were assigned to either one of two experimental groups (Differentiated Instruction or Differentiated Authentic Assessment) or to a comparison group. Using a concurrent mixed method design, data were collected and analyzed relating to (a) the effects on teachers and students of a staff development program focusing on differentiated instruction, and (b) the effect on teachers and students of a staff development program focusing on differentiated authentic assessment strategies. Results suggest that differentiation of instruction and assessment are complex endeavors requiring extended time and concentrated effort to master. Add to these complexity current realities of school such as large class sizes, limited resource materials, lack of planning time, lack of structures in place to allow collaboration with colleagues, and ever-increasing numbers of teacher responsibilities, and the tasks become even more daunting. (Contains 77 tables and 4 figures.)