This advice-column-style blog for SLPs was authored by Pam Marshalla from 2006 to 2015, the archives of which can be explored here. Use the extensive keywords list found in the right-hand column (on mobile: at the bottom of the page) to browse specific topics, or use the search feature to locate specific words or phrases throughout the entire blog.
Q: My client says Sf for initial S words, as in “Sfoap” for “soap.”
One simply has to hold the lower lip down and out of the way while practicing the words. This will prevent the lower lip from elevating to produce the F. I probably would have the client use his own fingers to hold the lip down.
I call a method like this an “inhibition” technique. You are inhibiting an unwanted movement. At the very least the child’s finger will help him feel the unnecessary lip movement.
I also would use a mirror so he can see the error. And I would spell it out for him. I would spell out “SFOAP” and show him that it should be “SOAP.”