Dual enrollment programs enable high school students to enroll in college courses and earn college credit. Once limited to high-achieving students, such programs are increasingly seen as a means to support the postsecondary preparation of average-achieving students and students in career and technical education (CTE) programs. This report seeks to answer several questions regarding the effectiveness of dual enrollment programs using statistical methods to examine the impact of dual enrollment participation for students in the State of Florida and in New York City. Particular attention is given to the impact of dual enrollment participation on students enrolled in CTE courses of study in high school. Evidence is provided to support dual enrollment as a useful strategy for encouraging postsecondary success for all students. Research questions for this study included investigation of initial entry to postsecondary education, and both short-term and long-term effects of participation in a dual enrollment program. Two existing large-scale administrative datasets were examined, using non-experimental methods, including ordinary least squares and logistic regressions. Findings for each program are discussed separately. In Florida, a positive relationship was found between dual enrollment participation and short- and long-term outcomes: (1) Dual enrollment was positively related to student likelihood of earning a high school diploma: (2) Participation in dual enrollment was positively related to enrollment in college; (3) Dual enrollment students were statistically significantly more likely to persist in college to a second semester; (4) Of students ever enrolled in postsecondary education, dual enrollment participation was positively associated with their likelihood of remaining enrolled two years after graduating from high school: (5) Dual enrollment students' grade point averages were statistically significantly higher than their non-participating peers throughout their postsecondary careers; and (6) Dual enrollment students had earned more postsecondary credits three years after high school graduation (indicating that they had made more progress toward a degree). Participation intensity had little impact on short- and long-term outcomes: the statistically significant effect of dual enrollment participation versus non-participation generally remained the same, regardless of whether students took one, two, three or four, or five or more dual enrollment courses. These finding were found true for all students. Though not as consistently as in Florida, positive short- and long-term outcomes of dual enrollment participation were also found in the New York City sample: (1) Program participants were more likely than their peers to pursue a bachelor's degree; (2) Program participation was positively related to students' first-semester grade point averages; and (3) Participation was positively related to students' overall progress toward a degree. Unlike Florida, some influence of participation intensity was found in New York, especially for long-term outcomes. Findings provide an encouraging, though not definitive, picture of dual enrollment as a strategy for encouraging student access to and persistence in postsecondary education. Further research is advocated to use additional control variables for student background and motivation. (Contains 6 footnotes, 7 figures and 29 tables.)