This volume examines the relationship between young children's degrees of bilingualism and features of the verbal input which these children receive from their parents. In particular, it seeks to explore the following question: to what extent are families who follow the 'one parent-one language' principle and whose children become active bilinguals this way, different from families who take the same approach but whose children never develop an active command of the minority language? Case studies of six first-born children growing up with German and English were done during the children's third year of life. The input the children received was examined for parents' consistency of language choice, parents' insistence that the children use the appropriate language, parents' sensitivity towards the children's interactional and attentional needs, and parents' orientation towards the teaching of formal aspects of the linguistic system. The findings support the notion that raising one's children bilingually according to the 'one parent-one language' principle involves great efforts on the side of the minority language-speaking parent. Importantly, they indicate that these efforts must be invested in the child's education turn-by-turn.