The study examined the impact of participation in an optional flexible year program (OFYP) on academic achievement. The ex post facto study employed an explanatory sequential mixed methods design. The non-probability sample consisted of 163 fifth grade students in an OFYP district and 137 5th graders in a 180-day instructional year school district. The multivariate analysis of the data showed that the 5th graders in the OFYP outperformed the 5th graders in the comparison group on the basis of mathematics, reading, and science group centroids. Analysis of the educators' qualitative data resulted in three themes, namely, 1) academic achievement, 2) focused instruction, and 3) negative aspects. The educators felt that the OFYP had a positive influence by increasing students' efforts and motivation. The quantitative and qualitative results were synthesized and discussed. Practical implications were presented. [The dissertation citations contained here are published with the permission of ProQuest LLC. Further reproduction is prohibited without permission. Copies of dissertations may be obtained by Telephone (800) 1-800-521-0600. Web page: http://www.proquest.com/en-US/products/dissertations/individuals.shtml.]