The Knowledge Is Power Program (KIPP) is a bold effort to create a network of charter schools designed to transform and improve the educational opportunities available to low/income families. KIPP schools seek to actively engage students and parents in the educational process, expand the time and effort students devote to their studies, reinforce students' social competencies and positive behaviors, and dramatically improve their academic achievement. Ultimately, the goal of KIPP is to prepare students to enroll and succeed in college. The KIPP Foundation is guiding this effort by selecting and training school leaders, promoting the program model, and supporting the KIPP network schools. This report presents preliminary findings from a matched, longitudinal analysis designed to estimate KIPP's effect on student achievement. The author's preliminary work estimates effects in 22 KIPP middle schools--making this the first report that applies a rigorous (nonexperimental) methodological approach across a nationwide sample of KIPP schools. They selected schools for which they were able to collect longitudinal, student/level data, and that were established by the 2005/06 school year or earlier to ensure that a minimum of two entering cohorts of students per school would be observed for multiple years. They find that students entering these 22 KIPP schools typically had prior achievement levels that were lower than average achievement in their local school districts. For the vast majority of KIPP schools studied, impacts on students' state assessment scores in mathematics and reading are positive, statistically significant, and educationally substantial. Estimated impacts are frequently large enough to substantially reduce race/ and income/based achievement gaps within three years of entering KIPP. They describe these findings in more detail in this report. Appendices include: (1) Administrative Data; (2) Supplemental Tables for Chapter II; (3) Analytic Methods; (4) Alternative Specifications; and (5) Subgroup Analyses. (Contains 34 tables, 21 figures and 28 footnotes.) [This paper was submitted to KIPP Foundation. For the accompanying report, see ED511108.]