In dual language programs, children who speak a majority language are grouped with children who speak a minority language, and instruction is delivered in both languages. This focus on structural rather than instructional design can lead to a recipe approach to design: add the ingredients (native-speaking children, content language instruction) in the proper amounts and expect the desired product (bilingual children). However, a certain type of linguistically mediated interaction is implicit in the equation, since children with different language proficiencies are expected to guide each other in the mutual process of language acquisition. The teacher is faced with the task of fostering these interactions. Based on a year-long ethnographic study of a dual language Kindergarten classroom, this paper describes and analyzes one teacher's efforts to design a physical environment to afford children's Spanish language conversation, the failure of these efforts, and the unexpected emergence of conversation through conflict and negotiation.