How does variability in children’s environments lead to variability in their language skills? We have been addressing this question through the use of natural experiments, true experiments and corpus-based studies. At the heart of this work are 140 infants whose language experience and communicative abilities we have been charting from 11 months to 4 years. I will illustrate when environmental effects do and do not hold for developments including the production of pointing gestures, early vocalisations, words, multiword speech and informative discourse. I will discuss how it is possible to identify causes of change across the preschool years through intervention studies and how the challenges that face us now lie in better characterising early communicative skill, particularly in the pragmatic domain.