Learning to decode is critically important to the process of becoming literate. As such, a thorough understanding of decoding development is critical as well. Extant theories contribute to such an understanding but do not provide a complete description of decoding development; a different theory is needed to address limitations in the extant theories. Overlapping wave theory (Siegler, 1996) provides a different description of cognitive development that has potential to further our understanding of decoding development. A theory that views decoding as a problem-solving, or word-solving, process could provide insights into the multiple ways of thinking in which children engage when learning to identify unfamiliar words and the nature of change in those ways of thinking. The purpose of this study was to describe the moment-by-moment nature of change in word-solving behaviors over nine weeks of tutoring and across increasingly difficult levels of text. Overlapping wave theory (Siegler, 1996) and literacy processing theory (Clay, 2001; as described in Doyle, 2013) provided the theoretical framework for the study. I used an extant dataset that included video recordings of the one-to-one tutoring sessions of eight students (grades 1 through 3) who were reading below grade level. Using a microgenetic design, I examined the students' word-solving behaviors during the assessment portion of the lesson for two out of the four lessons every week. I modeled the changing frequencies of each behavior and examined trends and relationships between the changing behaviors. I compared change between students who were reading at lower and higher levels of development and used qualitative analysis to more fully describe the changes for individual students. The results provide support for the use of overlapping wave theory and literacy processing theory to characterize word-solving development in early readers. Change in word-solving behaviors was continuous and non-linear and included evidence of relationships between the trends of different behaviors. Different behaviors changed at different points, with Rereading showing significant change for the lower-level readers and then stabilizing for the higher-level readers. The reverse was true for Attempting, which did not show statistically significant change for the lower-level readers but did change for the higher-level group. Individual profiles of progress further demonstrated the incremental and inconsistent shifts in behaviors over time as well as the unique paths each student took toward conventional literacy. Implications for theoretical descriptions of word-solving development, instructional considerations, and the use of microgenetic designs in reading research are discussed. [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.]