The purpose of the study was to determine the relationship between scores of the new teachers' classroom effectiveness with numerical indexes of mentor support, mentor infrastructure, and workplace ecology. In addition, this study sought to determine the effect of various demographics (i.e., gender, age, race, degree, teaching level, and certification route) on the Classroom Effectiveness Index (CEI) scores of first-year teachers, and to determine the differences, if any, between the Classroom Effectiveness Index scores of first-year teachers who remained on campus, switched campuses, or left the district. This study is primarily correlational in nature - looking for relationships between quantifiable variables. The subjects are 68 first-year teachers. The mandatory mentoring program the subjects were involved in consisted of a paid, veteran teacher who worked on the same campus as the first-year teacher and assisted in instructional or behavioral needs. This study measured the impact of the first-year teachers' mentoring experiences to the Classroom Effectiveness Index scores and teacher retention. The findings suggest that the Classroom Effectiveness Index scores might not be an appropriate tool for uncovering which aspects of mentoring contribute to student achievement and retention. Adding the value-added measurement tool to the categories of mentor support (MS), mentor infrastructure (MI), and workplace ecology (WE), rendered no statistically significant results. Therefore, further research is necessary to continue to define the effective characteristics of mentoring and its impact on classroom effectiveness and retention.