This causal/comparative study answered: Does the attainment of year-end kindergarten reading benchmark status vary between students enrolled in half-day kindergarten and those enrolled in full-day kindergarten after controlling for differences in initial instructional recommendations? The researcher analyzed the 2005-2006 achievement of 906 students who were enrolled in 53 kindergartens across ten different schools in an elementary district in the American Southwest. 25 classes were full-day and 28 were half-day. The beginning and end-of-year instructional recommendations yielded from the DIBELS formative assessment system revealed benchmark status. Binary Logistic Regression allowed the researcher to control for differences in the beginning-of-the-year instructional recommendation. Results revealed that a student enrolled in a full-day kindergarten was 3.235 times more likely to attain end-of-year benchmark status than a student enrolled in a half-day kindergarten. Two other findings were identified: (1) a student in the study was 12.629 times more likely to attain end-of-year benchmark status if they had achieved the beginning-of-the-year benchmark; (2) the odds were 40:1 against a student attaining end-of-year benchmark status if her or she was enrolled in a half-day and did not meet beginning-of-the-year benchmark 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.]