In 2007, using funds from the federal Teacher Incentive Fund (TIF) and private foundations, the Chicago Public Schools (CPS) began piloting its version of a schoolwide reform model called the Teacher Advancement Program (TAP). Under the TAP model, teachers can earn extra pay and take on increased responsibilities through promotion (to mentor teacher or master teacher), and they become eligible for annual performance bonuses based on a combination of their contribution to student achievement (known as "value added") and observed performance in the classroom. The model calls for weekly meetings of teachers and mentors ("cluster groups"), and regular classroom observations by a school leadership team to help teachers meet their performance goals. The idea behind TAP is that giving teachers performance incentives, along with tools to track their performance and improve instruction, will help schools attract and retain talented teachers and help all teachers raise student achievement. This report is the last in a series of reports providing evidence on the impacts of CPS' version of TAP, called "Chicago TAP." It presents findings from the four-year implementation period, with special emphasis on the 2009-2010 and 2010-2011 school years, the third and fourth years of the program's rollout in Chicago. Earlier reports (Glazerman et al. 2009; Glazerman and Seifullah 2010) provide detailed data on each of the first two years of the program, respectively. CPS implemented Chicago TAP as a pilot program intended for 40 high-need schools. The program began in 10 schools in the first year (cohort 1) with a rollout plan to add 10 more Chicago TAP schools (cohorts 2, 3, and 4) in each year of the TIF grant's four-year implementation period. The authors address three research questions regarding Chicago TAP: (1) How was the program implemented?; (2) What impact did the program have on student achievement?; and (3) What impact did the program have on teacher retention within schools? To assess the first year under Chicago TAP for schools that began the program in fall 2009 (cohort 3), the authors looked at how teacher development and compensation practices in Chicago TAP schools differ from practices normally implemented in CPS schools. The authors found that teachers in Chicago TAP schools reported receiving significantly more mentoring support than teachers in similar non-TAP (control) schools. This finding reflects the fact that under the Chicago TAP model, teachers are guided by mentor teachers, and cluster groups meet weekly. They also found that veteran teachers in Chicago TAP schools were more likely than their control group counterparts to provide mentoring support to their colleagues; this finding is consistent with the fact that under Chicago TAP, teachers have the opportunity to assume leadership roles and responsibilities as Chicago TAP mentor or lead teachers. Teachers in Chicago TAP schools (veteran and novice) were aware of their eligibility for performance-based compensation. The authors found that the amount of compensation they expected approached the amount that was eventually paid out; that is, the average expectation was about $900, and the actual amount paid out in bonuses to this group was an average of about $1,100 per teacher. They generally did not find evidence of an impact of Chicago TAP on teacher attitudes or school climate. While the introduction of Chicago TAP led to real changes inside the schools, the program did not consistently raise student achievement as measured by growth in Illinois Standards Achievement Test (ISAT) scores. The authors found evidence of both positive and negative test score impacts in selected subjects, years, and cohorts of schools, but overall there was no detectable impact on math, reading, or science achievement that was robust to different methods of estimation. For example, impacts on science scores overall (across years and cohorts) were positive, but not statistically significant unless they used one particular matching method that excluded some Chicago TAP schools from the analysis. The authors did find evidence suggesting that Chicago TAP increased schools' retention of teachers, although the impacts were not uniform or universal across years, cohorts, and subgroups of teachers. They found that teachers who were working in Chicago TAP schools in 2007 returned in each of the following three years at higher rates than teachers in comparable non-TAP schools. For example, the authors found that 67 percent of classroom teachers in cohort 1 schools in fall 2007 returned to their same school in fall 2010 compared to about 56 percent of teachers in non-TAP schools, an impact of nearly 12 percentage points. In other words, teachers in Chicago TAP schools in fall 2007 were about 20% more likely than teachers in comparison schools to be in those same schools three years later. When the authors looked at teachers who were working in schools that started Chicago TAP in later years, some of the impact estimates were not statistically significant. The authors also found some evidence of impacts on retention for subgroups of teachers, such as those with less experience, but the pattern of findings was not consistent. When they considered retention of teachers in the district, the authors did not find consistent evidence of a measurable impact. Given that Chicago TAP is a school-specific program, their main focus was on school-level retention, as opposed to retention in the district. Appended are: (1) Propensity Score Matching; and (2) Supplemental Tables. (Contains 32 tables, 6 figures and 27 footnotes.) [For related reports, see "An Evaluation of the Teacher Advancement Program (TAP) in Chicago: Year One Impact Report. Final Report" (ED507502) and "An Evaluation of the Teacher Advancement Program (TAP) in Chicago: Year Two Impact Report" (ED510712).]