As most children begin speaking and learning new words, errors may occur on several sounds. When errors persist beyond an expected age the child may have an articulation disorder. An articulation disorder is when a child has difficulty making specific speech sounds. When a child has one or more sounds in error he/she may be difficult to understand. Sounds can be omitted, distorted, or substituted. An example of an omission is "at" for "cat". When a child uses one sound in place of another sound, like "wamp" for "lamp" or "fumb" for "thumb" it is a substitution. Distortions are inaccurate productions of the intended sound.Errors with speech sound production may also be as a result of a phonological processing disorder. This involves patterns of sound errors. A child with a phonological disorder may substitute all sounds produced in the back of the mouth like /k/ and /g/ for sounds that are produced in the front of the mouth like /t/ and /d/. Another example of a phonological disorder is when all final sounds in words are omitted.
The links below provide information regarding typical speech sound acquisition and common phonological processes and the ages by which they should disappear.
Speech Sound Acquisition
Ages Phonological Processes Resolve
Information provided from the American Speech-Language Hearing Association (www.asha.org).