An exploratory study was conducted to identify the degree of language performance in native and bilingual English- and Spanish-speaking children under circumstances of native and bilingual language instruction. The study is a first step in testing the hypothesis that the underachievement of children in English-as-a-second-language programs and bilingual programs reflects an inadequate process of instruction. In those programs, the syntactical aspects of English is emphasized to the detriment of the children's conceptual development. Two hundred children, aged 9-12, in four groups (native English-speaking, native Spanish-speaking in Colombia, bilingual tested in English, and bilingual tested in Spanish) were administered a 33-item test based on a fable, and asked to interpret the story and answer questions. The results indicated that the native Spanish-speaking and native English-speaking children receiving instruction in their native countries performed significantly better than the bilingual groups receiving instruction in U.S. bilingual programs, and that all groups performed at much lower levels of abstraction than anticipated according to theory. The need for experimental research on the effects of instructional methods that use language as a mediating tool in conceptual development is suggested. (Author/MSE)