Most people picture one thing when they hear the word lisp: a child saying "thun" instead of "sun." That is one type, and it happens to be the type children are most likely to outgrow. The versions that tend to stick around are the ones parents are least likely to recognize by name.
That distinction matters, because it changes the answer to the question almost every parent asks first: do we wait, or do we do something about it?
The Four Types of Lisp
A lisp is a distortion — the sound is not swapped for another sound or dropped entirely, it is produced in an altered way. ASHA's clinical guidance on speech sound disorders groups distortions alongside substitutions, omissions, and additions as the four error types, and uses "a lateral /s/" as its example of a distortion. Clinically, lisps fall into four patterns:
- Interdental (frontal) lisp — the tongue pushes forward between the front teeth, so /s/ and /z/ come out as "th." This is the one everyone recognizes.
- Dentalized lisp — the tongue pushes flat against the back of the front teeth rather than through them. The sound is not quite a "th," but it is muffled and slightly thick.
- Lateral lisp — air escapes over the sides of the tongue instead of down a center groove. This is the "slushy" or wet-sounding lisp, and it is the one parents most often describe without having a word for it.
- Palatal lisp — the tongue makes contact too far back, against the roof of the mouth, giving /s/ a distorted, almost "hy" quality. This one is less common.
The split that actually drives decisions is this: interdental and dentalized lisps show up in typical speech development. Lateral and palatal lisps do not.
Which Lisps Children Outgrow
/s/ and /z/ are among the later sounds to settle into place, and a preschooler pushing the tongue forward on them is a common, unremarkable stage — especially while front teeth are coming and going. Many of those children resolve it without any therapy at all as their front teeth come in and their speech sounds mature.
So for an interdental lisp in a four-year-old, monitoring is a reasonable plan.
A lateral or palatal lisp is a different situation. Neither is a stage children pass through on the way to correct production, which means "he'll grow out of it" is not really on the table. Both involve a tongue posture that has to be retrained deliberately, and both tend to become more entrenched with time — every day of practice is a day of practicing the wrong pattern. When one of those is what you are hearing, waiting for a birthday does not buy you anything.
Here is the practical version: if the lisp sounds like "th," time may help. If it sounds wet, slushy, or oddly muffled, time will not.
How Common Is This?
Speech sound errors in general are far more common than most parents assume. ASHA's practice portal cites estimates that 2.1% to 23% of 4- to 6-year-old children have a speech sound disorder, that 3.6% of 8-year-olds have a persistent one, and that 1% to 2% of young adults still show residual or persistent speech errors. Boys are affected about twice as often as girls in grade school.
That last figure is worth sitting with if you are an adult who has quietly disliked your own /s/ for twenty years. You are not an outlier, and nothing about the timeline makes it too late.
The Tongue Thrust Connection
This is the piece that most often explains why a lisp did not respond to therapy the first time around.
ASHA's practice portal on orofacial myofunctional disorders states that "children with speech sound disorders are more likely to exhibit a tongue thrust swallow," and lists among the features of these disorders "distorted productions of /s, z/, often with an interdental lisp." It also notes abnormal tongue placement for a whole set of other sounds — /t, d, l, n/ and the "ch," "j," and "sh" sounds — in the same population.
The logic is straightforward once you see it. If the tongue rests forward and pushes against or between the teeth every time your child swallows — which is hundreds of times a day — then thirty minutes a week of practicing a correct /s/ is competing against a pattern being rehearsed all day long. The articulation drill is not wrong; it is outnumbered.
ASHA's guidance cuts both ways here, and it is worth being precise about it: the portal cautions SLPs against using myofunctional therapy on its own to fix speech sound errors, and says clinicians "may need to consider combining OMT and articulation interventions." Neither piece substitutes for the other. When both are present, both get addressed.
This is exactly the overlap Bloom is built around. Laura Friedman is both a certified speech-language pathologist and a Qualified Orofacial Myologist, so a lisp that turns out to be sitting on a tongue thrust swallowing pattern does not require a referral to a second provider and a second waitlist. If you want to see what that side of the work looks like day to day, our guide to tongue thrust exercises walks through the 4S method and the retraining sequence.
What Lisp Therapy Actually Involves
Articulation therapy for a lisp follows a well-worn progression, and there is a reason it has not changed much: it works, as long as each step is solid before the next one starts.
- Placement. Finding the correct tongue position for /s/ — tip up or tip down, teeth close together, a narrow center groove for the airstream — using mirrors, tactile cues, and a lot of listening.
- Isolation. Producing a clean /s/ on its own, repeatedly and reliably, before any word gets attached to it.
- Syllables. The sound in simple combinations, in all positions: "see," "sah," "us," "asa."
- Words. Then phrases, then sentences — each level only once the one before it is consistent.
- Conversation. The step that gets skipped most often and matters most. A perfect /s/ in the therapy room that vanishes at the dinner table is not a finished job.
For a lateral lisp specifically, most of the early work is about airflow direction rather than tongue position alone — teaching the air to travel down the center of the tongue instead of spilling over the sides. That is a different starting point than an interdental lisp, which is one of several reasons the evaluation matters before the drilling starts.
Where an oral motor component is involved, we may layer in PROMPT or oral placement techniques, which give the tactile input some people need to feel a position they cannot yet hear. There is more on the full range of sound errors we treat on our articulation disorder treatment page.
Lisps in Adults
Adults come to lisp therapy for concrete reasons: presentations, sales calls, interviews, teaching, a voice on video calls that they have never liked. The work is essentially the same progression, with one honest difference — the pattern has decades of practice behind it, so carryover into real conversation takes deliberate effort rather than happening by itself.
The advantage adults have is enormous, though. They practice without being asked, they can hear the difference themselves, and they know exactly which situations they want to sound different in. Adult speech therapy at Bloom is built around those situations rather than around worksheets.
Getting a Lisp Evaluated
An evaluation looks at which type of lisp you are dealing with, whether it appears on /s/ and /z/ only or spreads to other sounds, whether tongue resting posture and swallowing are contributing, and how much it is actually affecting the person — a confident nine-year-old and a nine-year-old being imitated at school are not the same case, even with the same lisp.
Sometimes the outcome is "monitor this and check back in six months." You will hear that if that is the answer. Our broader guide to the signs your child may need speech therapy covers what else an evaluation considers.
Sessions are available in person in Dallas and through online speech therapy nationwide. Lisp work is one of the areas where telehealth genuinely shines — a close camera view of the mouth shows tongue placement more clearly than sitting across a table does.
Frequently Asked Questions
What are the four types of lisp?
Interdental (frontal), where the tongue comes between the teeth and /s/ sounds like "th"; dentalized, where the tongue pushes flat against the back of the teeth for a muffled /s/; lateral, where air escapes over the sides of the tongue for a wet, slushy sound; and palatal, where tongue contact is too far back. The first two are often outgrown. The last two generally are not.
At what age should a lisp be corrected?
It depends on the type. An interdental lisp is common in preschoolers and often resolves as front teeth come in and speech sounds mature, so monitoring is reasonable. A lateral or palatal lisp is not a typical developmental pattern, so age is not a reason to wait.
Is a lisp caused by tongue thrust?
Sometimes, and the two often occur together. ASHA notes that children with speech sound disorders are more likely to have a tongue thrust swallow, and lists interdental /s/ and /z/ distortions among the features of orofacial myofunctional disorders. When both are present, both need addressing — neither one on its own is enough.
Can adults fix a lisp?
Yes. ASHA cites 1% to 2% of young adults as having residual speech errors, and adults often progress quickly because motivation and consistent practice matter more than age.
How long does lisp therapy take?
Many children make significant progress on an isolated lisp in three to six months with weekly sessions and home practice. Adults working on a long-standing pattern often need two to four months. A contributing tongue thrust usually extends that, because there are two things to retrain.
Can lisp therapy be done online?
Yes. Placement, airflow, and listening all come across clearly on video — often more clearly than in person, since the camera can sit right in front of the mouth.
Wondering About Your Child's /s/ Sound?
The fastest way to know whether you are looking at a stage or a pattern is to have someone listen to it. Schedule a free consultation with Laura Friedman, MS, CCC-SLP, QOM — in person in Dallas or online nationwide — to find out which type of lisp you are hearing, whether tongue posture is playing a part, and whether now is the right time to start.