Research on writing at the elementary level has shown that prior knowledge and task environment can have a significant effect on writing performance. In addition, there is preliminary evidence that suggests that children's development in writing may vary by genre favoring the narrative over expository genres (e.g., Olinghouse & Wilson, 2011; and Camp, 1993). One way to mitigate the effects of prior knowledge on topic and genre is through varying prompting conditions. The new Common Core writing assessment context requires students to write in response to texts read. To date, however, there are no studies that simultaneously examine the effects of genre and prompt condition in the elementary grades. This study examines the effect of two prompting conditions (supported and unsupported) on students' writing performance in multiple genres (narrative, persuasive and informational report) in order to assess the potential impact of the read aloud accommodation on these new types of writing assessments along with the effect of genre simultaneously. Findings show that at the 3rd grade level, students write best in the informational report genre over the narrative and persuasive genre, and that the read aloud accommodation positively affects writing quality. At the 5th grade level, the read aloud accommodation does not have a significant effect on writing quality. Based on the findings above, there are a number of implications for current testing policy and instruction. First, features of the prompt condition such as providing a common text, and audience and genre cues resulted in higher style, organization, conventions and mechanic scores for the informational report genre in the younger grades. This contradicts earlier findings that suggest at the elementary level, the narrative genre is more accessible. Accordingly, an effort should be made by test-makers and educators to provide students with these beneficial supports when designing tests and assignments particularly for expository genres. Second, given the observed benefit of the read aloud accommodation for students in the younger grades, test makers should consider designing tests that vary the degree of supports students are provided on the read and write response tasks as they progress through the grade levels.