The Knowledge Is Power Program (KIPP) is a network of charter schools designed to improve the educational opportunities available to low-income families. KIPP schools seek to boost their students' academic achievement and, ultimately, prepare them to enroll and succeed in college. This paper provides the most thorough analysis to date of the characteristics of students entering and departing KIPP schools, making use of longitudinal, student-level data from 22 KIPP middle schools and district schools in their surrounding communities. In Chapter II, the authors show that, on average, KIPP students are more likely to be black or Hispanic and have lower incomes than students in the surrounding school districts, but they are less likely to be English language learners or students with disabilities. Chapter III addresses attrition from KIPP schools. Students who transfer out of KIPP schools tend to have lower achievement than students who remain, but this is also true for nearby district schools: transferring students tend to be more disadvantaged than persisting students, regardless of what schools they attend. Chapter IV describes patterns of late arrival across the 22 KIPP middle schools in their sample. Supplemental tables are appended. (Contains 5 tables, 5 figures and 16 footnotes.)