WHAT ARE SPEECH SOUND DISORDERS?

Speech sound disorder (SSD) is an umbrella term used to describe the difficulty or delay some children have in the development and/or production of speech. Most children make some mistakes as they learn to say new words, but a child who does not say sounds by their expected ages may have a speech sound disorder. If a 3-year-old isn't understood by strangers about 75% of the time (90-100% for 4-year-olds) then a speech assessment would be recommended. There are different types of speech sound disorders depending on the cause of the difficulty and the type of difficulty the child is experiencing. Different speech sound disorders include:

Phonological delay which is used to describe children who are following a typical pattern of speech development but are demonstrating developmental phonological errors of sound substitutions or omissions that typically should have disappeared.
Phonological disorder which is used to describe children who do not follow the typical pattern of speech development. Children with a phonological disorder may produce sound errors when producing words that are not seen in the speech development of typically developing children.
Articulation disorder which is used to describe children who have difficulty making specific speech sounds and often involve substitutions of one sound for another (e.g. /w/ for /r/ as in "wabbit" for "rabbit") or sound distortions, such a frontal or lateral lisp.
Childhood Apraxia of Speech (CAS) is a rare motor speech disorder. Children with CAS have problems saying sounds, syllables and words not because of muscle weakness or paralysis, but because the brain has problems planning movements of speech. The child knows what they want to say, but their brain has difficulty coordinating and planning the muscle movements necessary to say those words. Children with CAS are often extremely difficult to understand.
Speech sound disorders can also be caused by structural differences (such as cleft lip/palate) or physiological deficits (such as dysarthria).