The general purpose of this study is to assess the effectiveness of Milwaukee's independent charter schools in promoting student achievement growth. Independent charter schools are authorized by non-school district entities and are considered "independent" because they are not a part of the Milwaukee Public School District (MPS). Specifically, the report presents the results of an analysis comparing achievement gains of independent charter students to the achievement gains of a group of matched comparison students attending MPS. Students were matched on prior achievement and propensity scores, which help to control for differences between students on observable characteristics. Based on three years of student achievement growth, charter school students outperformed MPS students in both reading and mathematics after controlling for baseline achievement and other student characteristics. Drawing upon the authors' earlier study of charter school gains (Witte et al., 2010), they see a clear pattern of positive charter school effects growing over time. Supplementary analysis revealed that conversion independent charter schools--schools that converted from private schools--as a subgroup did better than MPS schools in all three growth years. In the third growth year non-conversion charter schools also did better than MPS schools in mathematics but not necessarily in reading. Further analyses indicate that after three years charter schools appear to have the greatest positive impact on students at the lower end of the achievement distribution. When looking specifically at "stayer students", or those who remained in their initial sector (charter or traditional) for four years, the performance of charter stayers was much higher than that of MPS stayers after three years. Appended are: (1) Study Attrition; and (2) School Switching. (Contains 16 tables, 1 figure and 17 footnotes.)