Replication of the Second International Mathematics Study (SIMS) in Ontario, Canada, is described and assessed. The curriculum and testing program covers numerical methods, geometry, and algebra. Whereas classical studies focused on mean scores of a system's students and on percentages of teachers for opportunity to learn (OTL), SIMS aggregates student scores as attained coverage indices and these indices are nothing more than classical p-values. The SIMS approach aggregates OTL data into implemented coverage indices that are grounded in the same test items as attained coverage indices or p-values. The SIMS methodology also involves an intended coverage, which in the past has been labelled the approved curriculum. Results from various school boards and regions--Halton, North York, Scarborough, York, Durham, Carleton, East Parry Sound, Grey, Peel, and Halton Roman Catholic School Board--are discussed. Focus is on data for Halton, York, and Carleton. In Ontario, a fundamental shift from a focus on individual student differences in total scores to a new focus on group proportions of success on particular items is currently well underway but is not yet complete. SIMS replications identify some of the realities of changes that are possible when the right sorts of data are gathered and analyzed at a level that is close to the school and school members. The second generation of SIMS replications is currently underway. Four data tables and a flowchart model for the cyclic renewal/revision of a mathematics curriculum are provided. (TJH)