Researchers and practitioners need robust measurement tools for evaluating knowledge of child development to better support parents and their children during pregnancy and the transition to parenthood. We addressed this need by evaluating the psychometric properties of the Domains of Development Instrument (DoDI) for measuring knowledge of developmental milestones from birth to 3 years. We evaluated four types of validity evidence for the DoDI: test content, response processes, internal structure, and relations to other variables. We convened an expert panel to evaluate test content and conducted cognitive interviews with mothers to evaluate response processes. We also collected responses from a sample of 418 English-speaking pregnant women to evaluate internal structure and relations to other variables. We observed content validity and response process validity, as well as the predicted internal structure, internal consistency, test--retest reliability, and convergent validity. We conclude with recommendations for future research with the DoDI.