This paper reports a normative study on the phonological development of British English-speaking children. Speech samples of 684 children, aged between 3;0 and 6;11 years, randomly selected from nurseries and schools in eight different areas throughout the UK, were collected and analysed to obtain normative data. This paper reports on two aspects of speech development: the age of acquisition of sounds (phonetic acquisition) and the age that error patterns were suppressed (phonemic acquisition). It discusses the effects of age, gender and socio-economic status on speech sound development. The study found that older children had more accurate production and fewer error patterns in their speech. It found no gender differences in the younger age groups. However, in the oldest age group, it found the phonological accuracy measures of girls' better than boys. It found no significant effects of socio-economic status on any of the phonological accuracy measures.