Technological advances offer new ways and approaches to teaching and learning and have affected traditional methods of instruction and student assessment. Portfolio assessment is one way to document a student's progress over time and has been the subject of considerable research. This mixed method study explored the extent to which portfolio assessment enhances learning development in the area of reading for preschool children and whether portfolio assessment can improve teacher instruction in reading for preschool students. The participants included 30 preschoolers, three teachers, and one moderator. Quantitative data in the form of standardized reading grades from the creative curriculum assessment battery and reading grades of assignments contained in the portfolios for each student participant were collected. The data analysis consisted of a comparison of reading grades before and after the use of portfolio assessment. One-way ANOVA was used to analyze variability. Qualitative data were collected from interviews of participating teachers and the moderator. They were analyzed using an interpretive analysis framework consisting of four categories into which data from the interview questions were placed. The findings suggested that portfolio assessment increases learning development in reading in preschool children and has a positive effect on the reading development of preschool students and on the level and quality of teacher instruction in reading. The use of portfolio assessment with preschoolers benefits both society and the students because students are taught at a young age how to think critically, which improves their logic and problem-solving abilities, and will reduce the risk of academic failure and enhance academic achievement as they proceed through elementary school and high school. [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.]