With decreasing enrollment, decreasing funding for public school education, changes in family and societal needs, and the mandates of the No Child Left Behind Act, policymakers and school leaders are wrestling with reforms to the school calendar and instructional time spent in the classroom, with the goal of increasing student achievement. Improving student achievement has been the focus of school reforms regarding time, including the 4-day school schedule, block scheduling, year-round schools, and expanded learning time. This study looked at schools in the state of Colorado that have participated in the 4-day school schedule during the school years 2005-2008 and found that there were no effects of the 4-day school schedule on 3rd-grade reading, writing, and math scores compared to those scores in comparably sized schools operating on a more traditional 5-day schedule. In addition, there is no relationship between 3rd-grade Colorado Student Assessment Program (CSAP) assessments for 3rd-grade students on a 4-day or 5-day schedule. According to the study, 3rd-grade students attending a 4-day school week scored better than or equal to the state CSAP percentage proficient and above for 2005-2008. Quantitative research methods were used, data were collected, and the analysis added research to the effects of time on achievement. [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://bibliotheek.ehb.be:2222/en-US/products/dissertations/individuals.shtml.]