The majority of high-stakes tests from elementary school through postsecondary education include the timed impromptu essay as a measure of writing performance. For adolescents with writing disorders, this type of evaluation often presents a significant barrier. The purpose of the current study was twofold. First, we investigated the influence of handwritten, typed, and typed/edited formats of an expository essay on the quality scores received by students with (n = 65) and without (n = 65) dyslexia. Second, we examined the contribution of spelling, handwriting, fluency, and vocabulary complexity to the quality scores that students with and without dyslexia received on the same writing task. Analyses indicated that vocabulary complexity, verbosity, spelling, and handwriting accounted for more variance in essay quality scores for writers with dyslexia than for their typically achieving peers. Both group and individual student outcomes are reported to better understand the needs of struggling writers with dyslexia. Implications for assessment, instruction, and accommodations are discussed with an eye toward reform efforts that target improved teaching and learning.