Teachers often struggle to provide all students access to specific learning activities that work best for them--and what works best for some students will not work for others. Differentiating instruction makes sense because it offers different paths to understanding content, process, and products, considering what is appropriate given a child's profile of strengths, interests, and styles. This study focused on teacher efficacy as a way to explain teacher willingness to differentiate instruction. We found that a greater number of professional development hours in differentiation of instruction was positively associated with both teacher efficacy and the teacher's sense of efficacy beliefs. This study demonstrated that teacher efficacy is an important dimension in implementing the process of differentiation regardless of what level or what content area the teacher taught (elementary, middle, or high school). Implications and future directions for research are also discussed.