Writing from source text is critical for developing college-and-career readiness because it is required in advanced academic environments and many vocations. Scenario-based assessment (SBA) represents one approach to measuring this ability. In such assessment, the scenario presents an issue that the student is to read and write about. Before writing, lead-in exercises are presented to encourage the examinee to engage with the source materials and to model the process used in a classroom writing project. This study experimentally manipulated a middle-school assessment design to understand if (1) the lead-in/essay structure increased scores erroneously with a concomitant decrease in test technical quality, and (2) the presence of a single unifying scenario affected scores or score meaning. In general, the SBA design did not appear to artificially increase total-test or essay scores. As importantly, it functioned as well as, sometimes better than, the alternative designs in terms of the measurement characteristics examined.