This report is the fourth in a series of annual reports produced by the School Choice Demonstration Project (SCDP) that provides descriptive information about the schools participating in the Milwaukee Parental Choice Program (MPCP). A total of 115 schools participated in the MPCP for the entire 2009-10 academic year, with 20,899 students enrolled in the schools using MPCP vouchers. Generally speaking, MPCP students made up a large part of participating schools' total enrollment--the average school-level percentage of MPCP students in these schools was 81 percent. Sixty-seven percent of participating schools had student enrollments that were greater than 80 percent MPCP students, while 55 percent had MPCP enrollment percentages above 90 percent. Collectively, private schools participating in the MPCP in 2009-10 offered the full range of grade options, from Kindergarten to 12th grade. Eighty-nine percent of schools served elementary students, while 81 percent served middle school students. Twenty-eight percent offered high school. The average per pupil cost at participating schools in 2008-09, the most recent year for which data were available, was $7,692, while the maximum scholarship amount that year was $6,607. Eighty-two percent of the schools reported per-pupil operating costs higher than the maximum scholarship amount. For the 2009-10 school year, the maximum scholarship amount was lowered to $6,442. When adjusted for inflation, this amounts to the lowest maximum scholarship amount since the 1997-98 school year. Three appendixes present: (1) Details of Non-Respondents; (2) List of Schools that Participated in the MPCP for the Entire 2009-110 School Year; and (3) MPCP Participating Schools No Longer Receiving Public Funds, 2006-07 through 2010-11. (Contains 17 tables, 8 figures, and 7 footnotes.) [Additional support for this project was provided by the Robertson Foundation.]