This paper argues for establishing stronger links between educational effectiveness research and school improvement. It presents the results of a 3-year study investigating the impact of the dynamic approach (DA) to school improvement on promoting student achievement in mathematics. It explores duration (offering the DA for more than 1 year) and sustainability effects of the DA. A sample of 18 secondary schools in Cyprus participated in this study. Two experimental groups used the DA to develop their school improvement strategies. The first group employed the DA for the first 2 intervention years and was more effective than the control group in promoting mathematics achievement at the end of the 1st, 2nd, and 3rd year. Schools that made use of the DA for all 3 years were found to be the most effective at the end of the 3rd year. Implications for research, policy, and practice are discussed.