In Spanish-monolingual Colombia, social pressures push for access to early 50 = 50% Spanish-English medium instruction from the age of five. Parents and school administrators consider this the best way to achieve bilingualism. This article takes a first general look at the effects of this type of bilingual education on the Spanish and English oral narrative proficiency of 15-year-old adolescents. Data consist of 72 frog stories told following a picture-book (Mayer, 1969): 18 Spanish and 18 English stories from 15-year-olds with 10 years of bilingual education in a Colombian bilingual school constitute the main sample. The other 36 stories, 18 from 15-year-olds in Colombian monolingual schools and 18 from comparable English-monolingual adolescents from a high school in the Boston area, were used to compare the bilingual stories to monolingual productions. The range and variability of the stories in the bilingual group are discussed, as they are compared to the monolingual stories. General similarities and differences between Spanish and English monolingual and bilingual narratives are analysed. Bilingual stories in both languages show evidence of underdevelopment in relation to monolingual stories, as they are sparse in several linguistic variables that show narrative proficiency (i.e. description of events, evaluative language, logical connections). Qualitative discourse analysis is used to describe exemplary productions.