Common Core State Standards (CCSS) have renewed attention on writing instruction. This study investigates the impact of teachers’ use of the Six Traits Analytic Writing model on random stratified samples of upper elementary students from a low-income population. All students, on average, made significant gains in each of the six traits during the school year. However, students in the Six Traits group made significantly greater gains in the trait of voice. The Six Traits Model showed some promise in improving the writing achievement of a low-income population, a critical concern in the current context of CCSS implementation.