What does it take to change a school's mathematics achievement profile from low to one that is proficient and advanced? Is this transformed achievement profile sustainable? Such is the story presented here, in this three-phase case study of a K-8 urban charter school's mathematics program. The first phase discusses the school's mathematics program as it existed in 2006. The second phase discusses the contents and interventions implemented which transformed the student achievement scores over a period of 3 years (2006-2009) from low achieving to proficient and advanced. The third phase is a follow-up mixed-methods investigation that was conducted to determine whether the achievement was sustainable and how the program changed. The interventions designed and implemented over the initial 3-year period are discussed, as are the findings of the follow-up study. This is discussed with reference to impacting change in student achievement and its relative significance for future work.