Purpose: This study investigated the stability and growth of preschool language skills and explores latent class analysis as an approach for identifying children at risk of language impairment. Method: The authors present data from a large-scale 2-year longitudinal study, in which 600 children were assessed with a language-screening tool (LANGUAGE4) at age 4 years. A subsample (n = 206) was assessed on measures of sentence repetition, vocabulary, and grammatical knowledge at ages 4, 5, and 6 years. Results: A global latent language factor showed a high degree of longitudinal stability in children between the ages of 4 to 6 years. A low-performing group showing a language deficit compared to their age peers at age 4 was identified on the basis of the LANGUAGE4. The growth-rates during this 2-year time period were parallel for the low-performing and 3 higher performing groups of children. Conclusions: There is strong stability in children's language skills between the ages of 4 and 6 years. The results demonstrate that a simple language screening measure can successfully identify a low-performing group of children who show persistent language weaknesses between the ages of 4 and 6 years.