Courtenay Frazier Norbury, George Vamvakas, Debbie Gooch, Gillian Baird, Tony Charman, Emily Simonoff, Andrew Pickles

Language development has been characterised by significant individual stability from school entry. However, the extent to which trajectories of language growth vary in children with language disorder as a function of co-occurring developmental challenges is a question of theoretical import, with implications for service provision. SCALES employed a population-based survey design with sample weighting procedures to estimate growth in core language skills over the first three years of school. A stratified sample (n = 529) received comprehensive assessment of language, nonverbal IQ, and social, emotional and behavioural difficulties at 5-6 years of age and 95% of the sample (n = 499) were assessed again at ages 7-8. Language growth was measured using both raw and standard scores in children with typical development, children with language disorder of unknown origin, and children with language disorders associated with a known clinical condition and/or intellectual disability. Overall, language was stable at the individual level (estimated ICC = 0.95) over the first three years of school. Linear mixed effects models highlighted steady growth in language raw scores across all three groups, including those with multiple developmental challenges. There was little evidence, however, that children with language disorders were narrowing the gap with peers (z-scores). Adjusted models indicated that while nonverbal ability, socioeconomic status and social, emotional and behavioural deficits predicted initial language score (intercept), none predicted language growth (slope). These findings corroborate previous studies suggesting stable language trajectories after ages 5-6 years, but add considerably to previous work by demonstrating similar developmental patterns in children with additional nonverbal cognitive deficits, social, emotional, and behavioural challenges, social disadvantage or clinical diagnoses.