It has been suggested that the outcomes of curriculum reform depend on the implementation strategy and coherence making between the reform and school practice. This study examined how teachers perceived a national core curriculum reform implementation in terms of change management and knowledge sharing, and how these contributed to the perceived curriculum coherence and to school-level impact of the reform process over time. Survey data (N = 2447) were collected from teachers during the recent core curriculum reform in Finnish basic education. The longitudinal data were collected at three time points during the first three years of curriculum implementation. A cross-lagged path model was utilized to explore longitudinal relations between the variables. The results showed that knowledge sharing practices and perceived curriculum coherence had reciprocal effects over the first year. Moreover, both predicted the extent to which the reform process was considered to promote school impact in terms of meaningful development and teacher commitment, which facilitated higher levels of curriculum coherence and knowledge sharing later on. Change management did not seem to predict the other constructs -- yet, knowledge sharing facilitated evaluations of successful change management. The results provide new insights on supporting meaningful school development in large-scale curriculum reform.