Not all speech errors are created equal!
Many times children present with overlapping types of speech sound errors. It's so important to have a speech language pathologist do a thorough assessment to decide on the most appropriate approach for each individual child.
Trying to use an articulation approach , like teaching how to move the lips and the tongue to produce the sound correctly, will be not be as effective for a child who has a phonological disorder. It's not that he cannot say the word correctly, it's the way he uses the sounds in words ( the linguistic component) that he needs help with. The same is true the other way around. Many times children need some of both, however It's essential to find out where the issue is stemming from.
I love using this visual of linguistic based errors up in the brain and motor based disorders down at the mouth. Thank you @lynnwilliamsslp
For inspiring this visual!