The isolation of errors in the language of young children has led to general and interesting statements concerning the acquisition process. This chapter examines the notion of error itself from a sociolinguistic perspective. It suggests that the notion of error should be understood in light of the range of variants in use for the feature under consideration. The chapter demonstrates that the assessment of what counts as an error is affected by data collection methodology, in particular by the way in which adult linguistic norms are established. If formality of speech can be measured in terms of degree of attention to one's speech, then these circumstances of language use are relatively formal. The chapter relates these theoretical and methodological points to research carried out on Samoan language acquisition, and then focuses on selected features of children's language.