This paper examines the bilingual and biliteracy development of a group of children from Samoan and Tongan families over the transition to mainstream English-medium schools in New Zealand. The children attended Pasifika Early Childhood Education Centres in Auckland, New Zealand, which provided full immersion programmes in their L1 (either Samoan or Tongan). Development in a home language (L1) and in English (L2) was plotted over the six months prior to going to school and over the first year at an English-medium school in a programme with known features for effective teaching of early reading and writing in English. Before going to school (at 5.0 years), the children were developing as incipient bilinguals. An incipient biliteracy paralleled their bilingual development, although there were large variations in profiles on entry to school. After one month at school, there were indicators of faster progress in English and a slowing down of progress in L1, which was dramatically confirmed by the results at the end of the first year. The rapid growth of literacy and comprehension knowledge in English from 5.0 to 6.0 years reflected the effectiveness of the school programme. However, the resultant patterns suggested children were now "at risk bilinguals". The relationships between literacy in two languages weakened over the first year, suggesting the possible transfer effects from one set of literacy skills to another appeared to happen very quickly on entry to school.