Language data from the 2002 Paraguayan census ate analyzed in order to determine differential patterns of intergenerational transmission of Guaraní and Spanish. The census data are interpreted in light of the results of a survey of 168 bilingual parents on their language identity, language attitudes and language practices. In households identified by the census as Guaraní-dominant, a majority of children is reported to speak only Spanish. The vast majority of parents reports using a single language in the home. The sample that was surveyed for the language attitudes study consisted of couples who identified themselves as either Guaraní-dominant, Spanish-dominant or bilingual. Their language identity served as a predictor of parental pride in Paraguay's two official languages, attitudes toward the teaching of content in Guaraní or Spanish, and Guaraní speakers' support of monolingualism in either language. The monolingual ideology of Guaraní dominant speakers may explain the very low rate of bilinguals reported in Guaraní-dominant homes. In the census, mixed-language households reported very few bilingual children, but the survey data on parental attitudes and practices indicates that in such households both languages are transmitted to children. The nearly exclusive use of Spanish in public schools does not reflect the positive attitudes of parents from all language groups toward bilingual education, but the language practices of parents reflect the reality their children will encounter when they enter school. Extending bilingual education in rural districts is needed to mitigate the massive shift to Spanish documented in Guaraní-households.