Despite of an importance of monitoring progress in writing for early graders, little research has been conducted. In particular, this study examined the technical adequacy of picture-word probe, focusing on the sensitivity of growth rate, and grade and gender differences. In this study, 196 first and second graders from two elementary schools were participated. The main research method for analying longitudinal data such as CBM was LMER(linear mixed effects regression). In order to evaluate the sensitivity of growth rate, and gender and grade difference, MI(multimodel inferencermation)was used. This study showed that picture-word probe scores were sensitive to growth over time. In addition, grade and gender were related to intercept and slope. We discuss implication for practice and future research.