[Overton]Emergence vs. Mastery

by Valerie Johnston, MS, CCC-SLP

Children who are referred and treated for articulation disorders at an appropriate age generally experience better outcomes and have shorter durations of treatment than those who are not.

But what is an appropriate age? Although many factors need to be taken into account when answering this question, a major part of the answer can be obtained from various age-of-acquisition studies. These studies provide two types of data: mastery level and emergence level.

While mastery level data reflect the ages at which 90% of the children studied were able to produce specific sounds, emergence data represent the ages at which 50% of the children were able to produce the same sounds. The chart below presents the data obtained from an age-of-acquisition study that looked at the articulation development of children between the ages of two and eight. The bars begin at the emergence level (50%) and end at the mastery level (90%).

The bar begins at the age of customary usage (emergence), which is the age at which more than 50% of the children tested correctly produced a given sound in two positions of words. It ends at the mastery level, or the age at which 90% of the children tested produced the sound correctly in two positions.

from: Sander, E.K., (1972). When Are Speech Sounds Learned? Journal of Speech and Hearing Disorders 37:55-63.

A glance at the above chart makes it obvious that there is a considerable difference between the age at which a sound begins to emerge and the age at which it is mastered. For example, 50% of the children studied were able to produce the "r" sound at three years of age. However, it was not until three years later (at six years of age) that the mastery level was reached. The above chart reports group data, but the manner in which individual children develop speech follows a similar pattern, with sounds emerging in a few words and gradually progressing toward the mastery level of production.

When determining the appropriate age for production of a specific sound, one should focus on the emergence, or left side of the acquisition lines. In addition to providing a more accurate picture of the way children actually acquire speech, focusing on emergence levels eliminates a major problem with the mastery level data. This is that the data reported in these studies is group data, which means that it is possible that most children produced each sound correctly at a lower age and that only a few children caused the 90% level to be set at a higher age.

In addition to eliminating this possibility, focusing on emergence data makes it possible to stimulate production of age-appropriate sounds (i.e.: sounds that typically emerge at the child's age). In most cases, if emergence is stimulated, it is not necessary to teach each sound to the mastery level. Production of a specific sound can be stimulated, worked to a 50% emergence level, and reassessed at a later time to determine if further intervention for that sound is warranted. This allows the child to either move on to other error sounds or to be dismissed from formal treatment more quickly.

(For the results of another study on early sound acquisition, click here.)


Darley, F. L., (1978). Appraisal of Articulation. In Darley and Spriestersbach (Eds.), Diagnostic Methods in Speech Pathology (2nd ed.), 222-255, New York: Harper and Row Publishers.

Dunn, C., (1984). Phonological Processes. Presentation at Texas Speech-Language-Hearing Association Convention.

Prather, E. M., Hendrick, D. L., and Kern, C. A., (1975). Articulation Development in Children Aged 2 to4 Years. Journal of Speech and Hearing Disorders, 40:179-191.

Sander, E.K., (1972). When are Speech Sounds Learned? Journal of Speech and Hearing Disorders, 37:55-61.

Schwartz, R.G., (1986). Phonological System: Normal Acquisition. In Costello and Holland (Eds.), Handbook of Speech and Language Disorders, 25-74, San Diego: College Hill Press.

If you have questions or need more information you can contact me at:

Overton Speech & Language Center, Inc.
Fort Worth, TX
(817) 294-8408


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Copyright 2001 Overton Speech & Language Center, Inc.
Last revised: February 22, 2001