The term ‘normative data’ refers to data that characterize what is typical of a particular large group at a specific point in time. Such data provide summary descriptions of the group’s behavior. So, for example, in order to understand the order of acquisition of speech sounds, researchers have studied large groups of children and identified which particular speech sounds are used at what particular age. Their investigations, therefore, summarize what is typical of an average child at a particular age.
There are a number of early studies (Templin, 1957; Sander, 1972; Prather, Hendrick, & Kern, 1975) and a number of more recent studies (Grunwell, 1981; Smit, Hand, Freilinger, Bernthal, & Bird, 1990; Goldman & Fristoe, 2000) to draw on. A useful summary chart is shown in Figure 1. This represents combined data from Sander (1972), Grunwell (1981) and Smit et al. (1990). The left-hand edge of each horizontal bar represents the age at which 50% of children produce the particular consonant correctly and use it in their speech. The right-hand edge of each horizontal bar represents the age at which 90% of children have mastered the use of the particular consonant in their speech. As this diagram is constructed from different sources it should be treated with caution. Whilst it does provide insights into a plausible developmental sequence it should not be read as an invariant progression from one sound to another. Rather, it is a guide to a likely pattern of acquisition. You should also note that the diagram only shows data for consonants: vowels are generally considered to have been acquired by the age of 3;00 years.
Goldman, R., & Fristoe, M. (2000). The Goldman-Fristoe Test of Articulation. Circle Pines, MN: American Guidance Service.
Grunwell, P. (1981). The development of phonology. First Language, iii, 161-191.
Prather, E., Hendrick, D., & Kern, C. (1975). Articulation development in children aged two to four years. Journal of Speech and Hearing Disorders, 40, 179-191.
Sander, E. (1972). When are speech sounds learned? Journal of Speech and Hearing Disorders, 37, 55-63.
Smit, A., Hand, L., Freilinger, J., Bernthal, J., & Bird, A. (1990). The Iowa articulation norms project and its Nebraska replication. Journal of Speech and Hearing Disorders, 55, 779-798.
Templin, M. (1957). Certain language skills in children. Minneapolis: University of Minnesota Press.
Williamson, G. (2010) English speech sounds: phonemes, allophones, and variations in connected speech. [eBook] http://www.kalgoo.com. Accessed 09 March 2011.