A speech disorder is characterized by errors of articulation. Simply put, this means not pronouncing letters correctly. Some commonly mispronounced sounds are /s/, /th/, /f/, /l/, /r/, and /sh/. These errors can occur in the beginning, middle or ends of words. They may be occasionally produced correctly, but the majority of them are not. At times, these errors may make it difficult for your child to be understood, and they may become frustrated by that.