Stuttering is typically a developmental disorder beginning in early childhood and continuing into adulthood in at least 20% of affected children.[19][45] The mean onset of stuttering is 30 months.[3] Although there is variability, early stuttering behaviours usually consist of word or syllable repetitions, while secondary behaviours such as tension, avoidance or escape behaviours are absent.[47] Most young children are unaware of the interruptions in their speech.[47] With young stutterers, disfluency may be episodic, and periods of stuttering are followed by periods of relatively decreased disfluency.[48]