In this article, we comment on the significant contributions to science and to clinical practice made by Floccia et al.'s study of over 400 bilingual 2-year-old children. To science, this work contributes new findings on the linguistic factors that make some pairs of languages easier to learn than others and rich data on the environmental factors that influence bilingual development. Their results provide clues to the nature of the language learning process. To clinical practice, Floccia et al. contribute a new instrument for the diagnosis of risk for language impairment in bilingual children and a new method for the development of assessment instruments more generally. The experience-adjusted approach to norming that they illustrate here provides an example for others to follow. Their method holds promise for test development in many domains where the goal is to assess children's internal capacity but the evidence that is available in children's achievement is systematically influenced by environmental factors.