The purpose of this study was to evaluate the impact of using a combination of three Curriculum Associates' mathematics products: (a) "i-Ready® Diagnostic," (b) "i-Ready® Instruction," and (c) "Ready® Mathematics Core Curriculum" over use of "i-Ready Diagnostic" alone at grades K-5. Use of all three products in combination is referred to as the "Blended Core Mathematics" implementation. It was hypothesized student achievement on the "i-Ready Diagnostic" would be higher for students using "Blended Core Mathematics" with fidelity over use of "i-Ready Diagnostic" only. The Human Resources Research Organization (HumRRO), in collaboration with Century Analytics, implemented a quasi-experimental design (QED) at the level of rigor required to achieve a What Works Clearinghouse (WWC) rating of "Meets WWC Group Design Standards with Reservations." Propensity score matching was used to identify a set of comparison schools and students demographically similar to "Blended Core Mathematics" treatment schools. To examine impact, hierarchical-linear modeling (HLM) was conducted separately at each grade with student-level baseline mathematics achievement and school-level baseline mathematics achievement and select school demographics as covariates. Results suggested students in the "Blended Core Mathematics" schools who were using the program as intended performed statistically significantly better than students in schools using "i-Ready Diagnostic" only. The effect sizes for four of the six grades (K, 1, 2, and 5) were greater than 0.25, which is considered a large effect in educational research (Lipsey et al., 2012). The following are appended: (a) Ready Blended Core Mathematics logic model; and (b) Complete HLM coefficients. [This report was prepared for Curriculum Associates.]