We discuss generalizability (G) theory and the fair and valid assessment of linguistic minorities, especially emergent bilinguals. G theory allows examination of the relationship between score variation and language variation (e.g., variation of proficiency across languages, language modes, and social contexts). Studies examining score variation across items administered in emergent bilinguals' first and second languages show that the interaction of student and the facets (sources of measurement error) item and language is an important source of score variation. Each item poses a unique set of linguistic challenges in each language, and each emergent bilingual individual has a unique set of strengths and weaknesses in each language. Based on these findings, G theory can inform the process of test construction in large-scale testing programmes and the development of testing models that ensure more valid and fair interpretations of test scores for linguistic minorities. (Contains 2 tables, 3 figures, and 1 note.)