This study was designed to investigate the effects of the year-round calendar on student performance in Texas middle schools as measured by achievement on the Texas Assessment of Knowledge and Skills (TAKS) test. In the State of Texas, 15 schools served students in grades six through eight using the year-round calendar in 2009-2010. The 15 year-round calendar schools were paired with 15 schools using the traditional agrarian calendar that had similar student characteristics, chosen from schools on the Texas Education Agency (TEA) comparable group list. The raw scores for all students in both groups were requested from the TEA on all TAKS subject tests for grades six through eight in the 2009-2010 school year. The raw scores were analyzed using an independent sample t-test and Cohen's d to compare the raw score means of the students in year-round schools and the students attending schools using the traditional calendar. The findings reported a significant difference in the average test scores between students in year-round schools and students in traditional calendar schools. The higher mean scores were found for the students attending year-round schools. Scores were also analyzed statistically for specific student characteristics. Demographic populations were compared for the two student groups including gender, ethnicity, socio-economic status, special education participation, and Limited English Proficiency status. [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.]