Articulation and Phonology
Children may say some sounds the wrong way as they learn to talk. They learn some sounds earlier, like p, m, or w. Other sounds take longer to learn, like z, v, or th. Most children can say almost all speech sounds correctly by 4 years old. A child who does not say sounds by the expected ages may have a speech sound disorder. You may hear the terms "articulation disorder" and "phonological disorder" to describe speech sound disorders like this. (asha.org).
Most children make some mistakes as they learn to say new words. A speech sound disorder occurs when mistakes continue past a certain age. Every sound has a different range of ages when the child should make the sound correctly. Speech sound disorders include problems with articulation (making sounds) and phonological processes (sound patterns).
If children experience articulation issues in school, it becomes very difficult for them to do well in any subject. They often become too shy or frustrated to tell teachers what they are thinking or why they are struggling, leading to poor classroom performance. Articulation therapy can help students not only speak more clearly, but speak with confidence and become better students.