A pediatric client substitutes interdentalized sounds for s and z and says /θɪnk/ for sink; phonemic contrasts are intact. What is the most likely diagnosis?

• A. phonological delay
• B. articulation disorder
• C. consistent phonological disorder
• D. inconsistent phonological disorder

Answer: (B)

The key idea is distinguishing an articulation issue from a phonological one. Substituting interdental fricatives for s and z is a motor placement problem—a lispy production where the tongue position changes how the sound is formed. Saying /θɪnk/ for sink shows this kind of single-sound substitution, not a broader pattern across many sounds.

Because phonemic contrasts are intact, the child knows the difference between sounds and can use them correctly in principle; the trouble is just in producing the sounds with the right place and manner. In a phonological disorder, you’d expect systematic, across-the-board pattern errors that affect many sounds and/or a loss of contrasts. The error here is isolated, consistent, and motor-based, which points to an articulation disorder.