Middle school serves as a key milestone for pre-algebra mastery, enabling students to be successful in high school algebra. Yet, at the point when students should be transitioning from learning arithmetic to learning mathematics, many are unprepared in fundamental mathematics concepts that strongly predict algebra achievement. Because mastering pre-algebra concepts in middle school provides a foundation for future success, we examined the impact of a supplemental mathematics curriculum on student achievement called "Everyday Counts Algebra Readiness" (EDC) using a cluster randomized design in rural Mississippi schools. Previously, we presented the findings from the intent-to-treat impact study, which failed to yield statistically significant impacts of the EDC program on student achievement. For the current study, we turn to the issue of implementation. Specifically, using a treatment on the treated quasi-experimental design, we explored whether the EDC program had significant impact on student achievement when implemented with at least partial fidelity (at least 10 minutes, in 50 percent of observations). We also examined the relationship between level of implementation among treatment teachers and student achievement. Two outcome measures were used: 1) a McREL International (McREL)-developed assessment aligned to EDC content and 2) the Iowa Algebra Aptitude Test (IAAT), Fifth Edition. Results suggest that there were no statistically significant differences between treatment and control conditions scores on the IAAT when EDC was used with at least partial fidelity. This was also true for the McREL developed assessment. When examining the percentage of observations when EDC was used as a predictor of student achievement among only treatment teachers, results suggest a negative relationship, with more class time spent on EDC predicting lower achievement scores on the IAAT and the McREL assessment.