Too often, intervention occurs late, is fragmented, and is not supported by the system as a whole. Using traditional intervention structures, struggling students and the educators who support them are unlikely to achieve long-term success. What results is a precarious outcome--"can't do" students become "won't do" students. By the beginning of high school, years of struggle and basic skill deficits set the stage--high school students fail core classes. To be successful and sustainable, schools must have support systems that differentiate according to student needs. The most important rule is that one size does not fit all, meaning that students are provided what they need rather than what is necessarily prescribed at their given grade level. Lessons from schools with longstanding RTI systems suggest that differentiated systems must be established to carry out varying levels of instructional support to meet the needs of all students. Such a structure is designed around student needs, from the high-achieving student to the learning disabled. In this article, the author stresses that without intensive, targeted, and long-term interventions, students' major skill deficits cannot be successfully erased. Principals can decide how to arrange their building to support students and teachers. They can develop a tiered structure to support individualized student instructional needs that does not, by design, assume one size fits all.