We used mixed methods to examine differences in the early writing development of children, identified as at risk of literacy difficulties, in the context of Reading Recovery (RR). From an extant dataset of 24 children, we identified those who made fast progress (n = 6) and those who did not (n = 8). We studied change over time in the sources of information they used and problem-solving actions they took over the course of the intervention. We developed a writing rubric to analyze videos of writing interactions (280 min) and written messages (N = 674). Results demonstrated that the fast-progress group had higher end of intervention ratings for multiple dimensions of writing. HLM analysis showed that the fast-progress group had higher rates of growth in their use of sources of information (spelling and letter-sound relationships) and observable problem-solving behaviors. Fast- and slow-progress groups did not differ in what they wrote but, for both groups, dips in legibility coincided with increased linguistic complexity. By juxtaposing descriptions of writing development for both groups, results provide useful information for instruction and intervention.