The establishment of new towns in the twentieth century in many parts of the world is a test bed of koineization, the type of language change that takes place when speakers of different, but mutually intelligible language varieties come together, and which may lead to new dialect or koine formation. This article presents the case of Milton Keynes, an English new town designated in 1967. Our study investigated the speech of a sample of 48 working-class children divided into three age groups: four, eight, and twelve years of age, along with one caregiver for each. We hypothesize that the formation of a new dialect is in the gift of older children. We also hypothesize that dialect leveling, which is part of koineization, will be more rapid in a new town than in an old-established town. Detailed quantitative results for four vowels strongly support these hypotheses. At the same time, we investigate the social network types contracted by new town residents. We found many to be socially isolated locally, but that they maintained contacts with their place of origin. We show that migrants violate what the Milroys argue to be the normal inverse relationship between socioeconomic class and social network density: migrants have uniplex networks, while still having a low socioeconomic status. The consequences for dialect change are considered.