A “lisp” usually refers to a child's difficulty producing the /s/ and /z/ sounds because of incorrect tongue placement. With a frontal lisp the tongue is sticking out between the front teeth and the S sound becomes voiceless TH as in the word 'thumb' and the Z sound becomes voiced TH as in the word 'this.' If your student or child says the word 'sink' and it sounds like 'think' or if he says the word 'boys' and it sounds like 'boyth' he or she is probably exhibiting a frontal lisp. A good place to start in reducing this pattern is to bring it to their attention. You could let them know that when, "You said I want some, it sounded like you said I want thumb." An explanation that "I think you may be pushing your tongue out too far on the S sound" is a good way to explain this in simple terms. Then try the following easy strategies to get the child to produce the S or Z correctly.
*One of the easiest methods is to tell the child to “bite, smile, and blow.” This can help the child learn to keep the tongue behind the teeth.
*Ask the child to say the /t/ sound and hold that sound, and then “blow more air through the /t/ in order to produce a ‘Long T’” This helps the child find where to place the tongue for the /s/ and /z/ sounds and say an approximation of /s/.
*Have the child say the sounds “th-s-th-s-th-s-th-s…” in one long breath to increase awareness of the tongue tip and its placement.
These simple techniques can be used in the home or classroom quickly and will help begin the process of awareness for your student or child which is the first step. From there frequent modeling and correcting at appropriate times will help the student continue to improve on production of the S and Z sounds.