As part of a large-scale study of children's development, 7390 children were assessed on a range of speech tasks. These were used to identify three groups of children with speech errors within the sample: persistent speech disorder (PSD); speech errors but below the threshold for classification as persistent speech disorder (non-PSD); and common clinical distortions only (CCD). These three groups were compared on demographic factors, performance on IQ, non-word repetition, and diadochokinetic tests. Findings showed that the PSD group and the non-PSD group were most similar for gender, socio-economic status, IQ, and non-word repetition. In the diadochokinetic tasks, the PSD group and the CCD groups were more similar. Implications for these findings in terms of clinical practice are discussed.