## Core Concept
Dysfluency of speech, commonly known as stuttering, is a speech disorder characterized by the repetition or prolongation of sounds, syllables, or words, as well as interruptions or blockages in speech. In children, a period of dysfluency is considered a normal part of speech development.

## Why the Correct Answer is Right
The correct answer, **2-4 years**, corresponds to the age range when children often experience a period of speech dysfluency as they develop their language skills. During this period, children are rapidly expanding their vocabulary and sentence structures, which can lead to temporary speech difficulties. This normal dysfluency is usually seen as a part of language development and often resolves on its own.

## Why Each Wrong Option is Incorrect
* **Option A:** Speech development milestones are typically assessed from birth up to 5 years, but significant dysfluency is not usually expected before **2 years** of age as a normative phenomenon.
* **Option B:** While some children may still exhibit mild dysfluency around **4-5 years**, the peak period for normal dysfluency is generally considered to start earlier.
* **Option D:** **5-6 years** is generally considered late for the typical period of normal speech dysfluency; if dysfluency persists beyond this age, it may indicate a more persistent speech disorder.

## Clinical Pearl / High-Yield Fact
A key point to remember is that while some degree of speech dysfluency is normal in young children, particularly between **2-4 years**, persistent dysfluency beyond this age or dysfluency that causes significant distress or impairment may require evaluation by a speech-language pathologist.

## Correct Answer: C. 2-4 years.