Articulation disorders focus on errors (e.g., distortions and substitutions) in production of individual speech sounds. 

Phonological disorders focus on predictable, rule-based errors (e.g., fronting, stopping, and final consonant deletion) that affect more than one sound. 

It is often difficult to cleanly differentiate between articulation and phonological disorders; therefore, many researchers and clinicians prefer to use the broader term, "speech sound disorder," when referring to speech errors of unknown cause. 

How to Work on Your Child's Articulation At Home