How is early language development affected by the number of speakers infants are exposed to in their daily lives? Some infants spend most of their waking time with only one person, while others hear many different speakers. These children receive quite different input. Even if the very same words are spoken, these words are pronounced very differently when not one but multiple people spoke them. Laboratory studies point to a significant effect of such variability in the context of a short experiment: When infants hear multiple speakers, their ability to recognize the same word is hampered, whereas learning sounds and words improves. It remains an open question whether long-term exposure to multiple speakers in daily life helps or hinders language acquisition, as current theories lead to opposing predictions. This project combines experimental approaches with computational modeling. It will shed unprecedented light on how speaker variability in daily life affects language development, a question that has substantial implications for theories of language acquisition and for current diagnostic practices.