Previous research has demonstrated that writing instruction can support reading achievement (Graham & Hebert, 2011); however much of this work involved carefully designed interventions. In this study, we evaluated a conceptual framework of the direct and indirect effects of typical writing instruction and student writing practice on reading achievement in first grade. Fall reading, vocabulary, and writing data were collected from 391 students, and classroom writing instruction and student writing practice were observed in 50 classrooms. The effects of writing instruction on spring reading achievement were evaluated using a 2-level, fixed effects structural equation model. In a multiple mediator model, the total indirect effect of composing writing instruction through student writing practice on spring reading achievement was positive and statistically significant (ß = 0.17, p = 0.029), with a modest effect of composing writing instruction mediated by generative writing practice (ß = 0.15, p = 0.024). The final model explained 86% and 59% of the variability in spring reading achievement at the student and classroom levels, respectively. These results suggest that generative writing practice mediates the relationship between composing instruction and spring reading achievement. The results also highlight some potentially positive effects of typical writing instruction and student writing practice after controlling for reading instruction and fall reading achievement.