No study has comprehensively examined what types of students are attending new small schools in New York City and whether these students have different characteristics, on average, than students at the schools they replaced. This study fills this gap by comparing the characteristics of entering new small high school students with those of all other New York City high schools, as well as directly comparing the student composition of the new small high schools with the large high schools they replaced. The authors focus on student characteristics such as gender and socio-economic status, proficiency in eighth-grade reading and math, middle school attendance, whether students are over-age for their grade, and special education and English language learner classification. Across the various measures of entering students' characteristics, the story the authors observe is more one of stability than of change in the extent of segregation among schools in a given borough. At the beginning of this decade, there were moderate levels of segregation among schools in the concentration of students with various academic and social factors that presaged trajectories of success or failure. At the end of the decade, after the expansion of small high schools in many of the five boroughs of New York City, the amount of segregation was largely unchanged, with the significant but puzzling exception of students' free/reduced-price lunch eligibility. Overall, the authors see little evidence that the expansion of small high schools in New York City, including the replacement of large comprehensive schools with smaller schools on the same campus, fundamentally redistributed students throughout the system. Appended are: (1) Data and Methods; and (2) Results from Regression Models. (Contains 13 figures, 13 tables and 13 footnotes.) [For "Do New York City's New Small Schools Enroll Students with Different Characteristics from Other NYC Schools? Executive Summary. Education Policy for Action Series," see ED522166.]