Current reading research largely focuses on word reading. This study complements that focus by considering what children do when encountering unknown words and how that problem-solving changes over time. We used overlapping wave theory to describe how children who were having difficulty with reading changed their word-solving actions across nine weeks. A microgenetic approach using 18 timepoints provided a description of moment-by-moment change, finding that word-solving actions were variable and changed continuously in adaptive and increasingly sophisticated ways. Findings support the use of overlapping wave theory to characterize children's use of word-solving actions and have implications for research and instruction.