This report focuses on the initial design, implementation and baseline results of the five-year Longitudinal Educational Growth Study (LEGS) of the Milwaukee Parental Choice Program (MPCP) being conducted by the School Choice Demonstration Project (SCDP). The LEGS will be the first evaluation of the participant effects of the MPCP using student-level data since the initial pilot program expanded dramatically in 1995. Included in this initial report are baseline descriptions of achievement tests for a representative sample of MPCP students in grades 3 through 9, as well as outcomes for comparable samples of students in Milwaukee Public Schools (MPS). Also included are a descriptive analysis of survey results of MPCP parents and a carefully matched sample of MPS parents as well as a brief description of the results of student surveys for both samples. The first section of the baseline report discusses the construction of a sample of 2,727 MPCP students in grades 3-9. The report also discusses the selection of 2,727 similar Milwaukee Public School students. For both samples the core of this longitudinal study will be to track educational progress through school year 2011-12. The authors demonstrate that the sample of MPS students constructed by the SCDP is more similar to the representative MPCP sample along demographic and initial achievement criteria than other potential comparison groups of MPS students. Because this is a baseline report, readers should infer no causal links between participation in MPCP and test score outcomes. Five appendices are included: (1) Description of the Study Mandate; (2) Constructing the Sample for Study; (3) Data Collection Procedures and Protocols; (4) Parental Survey Tables; and (5) Student Survey Tables. (Contains 3 figures, 6 tables and 17 footnotes.) [For "Milwaukee Longitudinal School Choice Evaluation: Annual School Testing Summary Report. SCDP Milwaukee Evaluation Report #4," see ED508634. This report was also funded by the Kern, Robertson, and Walton Family foundations. ]