Q: My client is beginning to use S-blends, but she does so with an interdental lisp. Do I treat the phonological process first and let her lisp, or treat the lisp first and then the process? Or should I do both concurrently?  I am worried about reinforcing the lisp.

I would work on the phonology first to stimulate the use of the phoneme within the language.  Then I would address place of articulation.  That’s the way I would organize it in my head, at least, because that’s the way it evolves in normal development.  For example, it is very common for a two-year-old to develop plural (Hats, cats…) with interdental tongue placement on S. The child gets the phonological pattern first, and then she sorts out place of articulation.

Having said that, I would be stimulating normal oral stability all the way along, but I will not describe that process here.  That way, as the S emerges, it will be produced in a stabile way –– with the jaw high and the tongue in.