This research will evaluate several widely held but largely untested assumptions underlying current theory and clinical practice in childhood stuttering. These assumptions are based on the notion that children's production of various types of speech disruptions (speech errors, normal disfluencies, and stuttered disfluencies) are influenced by certain characteristics of their speech, such as the length and complexity of their utterances (linguistic characteristics), and their speaking rate and response latency (paralinguistic characteristics). The research design includes five studies that will systematically evaluate the relationship between children's speech characteristics and their production of speech errors, normal disfluencies, and stuttered disfluencies by measuring change in children's fluency while experimentally manipulating: (a) children's utterance length and syntactic complexity (Study l), (b) children's speaking rate and response latency (Study 2), and (c) children's conversational partner's speech characteristics (Study 3). in addition to examining factors that affect children's fluency, this research will evaluate explanations for the underlying cause of speech disfluencies proposed in recent theories and attempt to objectively differentiate between disfluencies judged to be normal vs. stuttered, based on the acoustic characteristics of the moment of speech interruption (Study 4). Finally, to more fully examine the role speech motor abilities play in children's production of speech disfluencies, children who stutter and children who do not stutter will be compared in terms of the rate, accuracy, and fluency of their oral motor movements in an expanded diadochokinetic task (Study 5). Results from these studies will help evaluate and refine prominent theories of stuttering by evaluating key assumptions about the factors affecting children's fluency and by examining the differences between normal and stuttered disfluencies. Results will also help improve the diagnosis and treatment of children who stutter by helping clinicians evaluate different types of speech disruptions most indicative of stuttering and by evaluating several assumptions at the heart of prevailing treatments for childhood stuttering.