This study hypothesized that HISD prekindergarten participation consistently correlated with better educational outcomes for students. Taking into account students' age differences through kindergarten enrollment, propensity score matching controlled for students' background characteristics. Three cohorts of students in this study were eligible or attended HISD prekindergarten during the 2001-2002 (Cohort I), 2002-2003 (Cohort II), and 2003-2004 (Cohort III) academic years. The study found that kindergarten students in Cohorts I, II, and III outperformed students who did not attend HISD prekindergarten on nationally-normed Stanford and Aprenda reading and mathematics tests, indicating a statistically significant positive effect of HISD prekindergarten in the short-term. HISD prekindergarten had extended effects for Cohort II students, given that they consistently outperformed non-HISD prekindergarten students at targeted grades third, fifth, and seventh. Long-term effects related to college preparedness on the PSAT, SAT, and ACT reading and mathematics tests were mostly in favor of non-HISD prekindergarten students; however, these results were not consistently significant. A higher proportion of HISD prekindergarten students demonstrated school persistence, having graduated on-time at 12 years, with significantly lower dropout rates compared to non-HISD prekindergarten students. Attendance rates at each level of measurement were significantly in favor of HISD prekindergarten students. The findings demonstrated that educating at-risk students during their early years has benefits. Evidence that continued support is needed for these students was also shown as they progress through school. Future research is needed to determine whether full-day HISD prekindergarten provides more lasting educational effects for students and to track their progress to ensure that the instructional model continues to build students' knowledge and skills.