SCALES is the first United Kingdom (UK) population study of language development and disorder at school entry and involves more than 180 schools across Surrey, UK. This study was initially established to determine the extent to which 'Specific' Language Impairment (SLI) was prevalent in a population (as opposed to clinically ascertained) sample at school entry and the impact of language impairment on other aspects of development, and how these patterns of development change over time. Over 7,000 children aged 4 years, 9 months, to 5 years, 10 months, who started reception class in state-maintained schools in Surrey in 2011 participated in the baseline self-administered questionnaire. A subsample of the children were followed up in Year 3 (aged 7-8), Year 6 (aged 10-11) and Year 8/9 (aged 12-13). The SCALES study ended in 2020.