Objective <p>The dearth of tools to quantify and track growth in social communication ability has been a barrier to understanding and monitoring treatment outcomes for neurodevelopmental disorders. We undertook a multi-staged, multisite study to create the Developmental Assessment of Social Communication Ability (DASCA), a new measure explicitly developed as a clinical outcome assessment for monitoring change—both over the course of development and in response to treatment.</p> Methods <p>The DASCA is a caregiver-report instrument created using a mixed-methods approach. Qualitative components of this approach included focus groups and cognitive debriefing interviews. Quantitative components included dimensionality analysis, differential item functioning, and item response theory modeling. The item bank was iteratively refined to assess social communication skills that are typically acquired by early- to middle- childhood.</p> Results <p>The final DASCA item bank contains 184 items. Expressive language was a major factor in determining the appropriateness of some items for certain groups of children. Negligible differential item functioning, primarily by age, was observed for some items. However, impact analyses determined that this differential item functioning did not meaningfully impact overall scores.</p> Limitations <p>Given that sample size limitations prevented us from using separate samples for exploratory and confirmatory phases of modeling, it will be important to gather additional validity evidence in independent samples, especially as the current data were collected during the COVID-19 pandemic.</p> Conclusion <p>The DASCA holds promise as an outcome measure for assessing changes in social communication ability. Ongoing development efforts include creating a computer adaptive test administration to allow for serial assessments using different item sets to yield a consistent score that is sensitive to change.</p>