Q: My preschool client backed all lingua-alveolars until I taught him D. But not — it is distorted (his tongue looks funny) and the other sounds aren’t coming. Help!

Most kids with a restricting lingua frenum use what the elocutionists used to call “thick speech” meaning that it was speech produced without the tongue bowled.  The tongue was humping, bulging, or what the researchers today would call arching upward.

This is probably what your client is now doing on D, and he will do the same on all lingua-alveolars until he gets the frenum surgically removed (clipped).

I would recommend the surgery. Here is more info from the blog on this important topic.