Differences in definitions (and underlying concepts) of "language-minority children at risk" and how these differences affect the results of research on the numbers needing special services are examined in this document. Citing the 1974 Amendments to the Bilingual Education Act as the beginning of a Federal effort to estimate the numbers and particular needs of students lacking in English proficiency, the paper focuses on four subsequent surveys: the 1976 Survey of Income and Education; the 1978 Children's English and Services Study; the 1980 Census; and the 1982 English Language Proficiency Study (ELPS). Discussion centers on the studies' varying notions concerning the impact of mother tongue, ethnicity, and socioeconomic status on a child's ability to learn a second language. In general, language background and usage are imperfectly related to English language proficiency. To assure that the needs of all limited-English-proficient language-minority children are met, definitions which are not restricted by concepts of language dominance or usage, and methods of identification which are not limited to the examination of English-speaking skills, must be used. The ELPS offers a new and powerful tool to update the estimates of the number of language minority children. The paper concludes with a list of sources of additional information. (KH)