A study investigated the notion that bilingual students' low academic achievement may be due to semilingualism (having limited language skills) in each of the two languages, and the cognitive deficits that presumably result. The subjects were two boys and two girls from the fifth and sixth grades with low proficiency in either English or Spanish. Data were drawn from observations and audiotaping of natural and structured conversations and interviews were conducted with each family to provide information on the students' language performance both within and outside school. No evidence emerged that any subject mixed Spanish and English, but all code-switched and could sustain discourse exclusively in either language when requested. All lacked vocabulary items in both languages. Three had greater strengths in Spanish than English, with vocabulary lacking primarily in school-related areas. All spoke English with a Spanish accent and used Spanish intonation patterns. Each had different strengths across settings in both languages, but was most able in small-group activities. All had negative feelings about Spanish, and all showed some signs of semilingualism. The findings strongly confirmed that teachers perceive their students as limited and adapt the instructional program to suit that perception. Second language education should de-emphasize deficits and focus on competencies. (MSE)