A frontal lisp, where the tongue pokes between the teeth so that “sun” sounds like “thun”, is common in young children and can be a normal part of development until around age 4 to 5. A lateral lisp, where air escapes over the sides of the tongue and s sounds wet or slushy, is not part of typical development at any age. Both types usually respond to therapy, and a registered speech-language pathologist can tell you which one your child has.
What a lisp is
The s and z sounds are made by placing the tongue tip just behind the upper front teeth, forming a narrow groove down the middle of the tongue, and sending a thin stream of air straight down that groove. The air hits the edges of the teeth and makes the sharp “hiss”. The sounds sh, ch, j and zh use a similar airstream a little further back.
A lisp is any distortion of that airstream. The ASHA Practice Portal classifies lisps as distortion errors rather than substitutions. The child is not swapping one sound for another by rule. They are producing the right sound with the tongue in the wrong place, so it comes out blurred. This matters because distortions are treated differently from the pattern-based errors described in our guide to phonological processes.
The types of lisp
| Type | What you hear | What the tongue does | Part of typical development? |
|---|---|---|---|
| Frontal (interdental) | “thun” for sun, “theebra” for zebra | Tongue tip pushes between or against the front teeth | Yes, commonly until around 4 to 5 |
| Dentalized | A dull, muffled s, not quite th | Tongue tip presses against the back of the front teeth | Often, usually mild and often resolves |
| Lateral | A wet, slushy s or sh, sometimes with spit | Air escapes over one or both sides of the tongue instead of down the centre | No, at any age |
| Palatal (less common) | A soft, sh-like s | Middle of the tongue rises toward the hard palate | No, at any age |
The frontal lisp is the one most people picture. It is the same tongue position as the English th sound, which is why the two sound alike. The dentalized lisp is a milder version. Many parents never notice it, and it often sorts itself out as the child’s s matures.
The lateral lisp is different. The sides of the tongue, which should seal against the upper back teeth, drop and let air leak out sideways. The result sounds slushy and may affect s, z, sh, ch and j together. Because it is not a step on the normal path to a clear s, clinicians generally treat it as a pattern that needs direct work rather than something to wait out.
When a lisp is developmental and when it is not
In the review by Crowe and McLeod (2020), 90 percent of children produced s correctly by a mean age of 51 months (4;3) and z by 57 months (4;9). Before those ages a frontal lisp is within the range of normal, and plenty of 3-year-olds have one. Caroline Bowen’s summary of phonological processes, widely used by SLPs, likewise lists the interdental pattern as one that typically fades in the preschool years.
As a rough guide:
- Age 3. A frontal lisp is common. Hearing and dental checks are sensible if you have other concerns, but therapy for the lisp itself is rarely the priority.
- Age 4 to 5. Many frontal lisps have resolved. If one is still present at around 4 and a half to 5, an assessment is reasonable, and this is often when therapy starts because children at this age can follow the instructions involved.
- Age 6 and up. A frontal lisp that persists into the school years is unlikely to disappear without help. Losing the front baby teeth can also bring a temporary lisp back for a few months.
- Any age. A lateral or palatal lisp is not expected to resolve on its own. An SLP may still choose to wait until the child is old enough to take part in therapy, but the pattern itself is not developmental.
These ages describe when therapy is typically considered, not deadlines. Earlier support is generally easier, and an assessment gives clarity either way.
Common causes
Most lisps have no single cause. Several factors can contribute, and an SLP looks at all of them during an assessment.
Tongue resting posture and tongue thrust. Some children rest the tongue low and forward in the mouth and push it forward when they swallow. The ASHA Practice Portal on orofacial myofunctional disorders notes that this forward pattern often goes along with a frontal lisp. Prolonged thumb sucking or pacifier use can encourage the pattern, as can habitual mouth breathing from allergies or enlarged adenoids.
Teeth and jaw. An open bite (the front teeth do not meet), a large overjet, or gaps from lost teeth give the tongue room to slide forward. Dental and orthodontic treatment sometimes helps, although therapy can usually proceed in the meantime.
Hearing. The s sound is high-pitched and quiet. Mild hearing loss, or fluid in the middle ear from repeated ear infections, can make it hard to hear clearly, which makes it hard to copy. A hearing test is a standard part of the picture.
Learned motor habit. Often there is nothing structural at all. The child simply settled into a tongue position early on and it became automatic, which is why practice can change it.
What therapy involves
Therapy for a lisp follows a traditional articulation approach. The ASHA Practice Portal describes it as a step-by-step sequence that moves from the sound on its own to everyday conversation.
- Assessment. The SLP listens to s, z and related sounds in all word positions, checks how the tongue, lips, teeth and jaw move, and tests whether the child can produce a clear s with cues (stimulability). They also screen hearing and language.
- Establishing the sound. The clinician finds a way for the child to produce a clear s. Common cues include “teeth together, smile”, keeping the tongue behind the teeth, starting from a t and letting the air out slowly (“t-sss”), or using a mirror and a straw to feel the airstream. For a lateral lisp the first step is often learning to send air down the middle rather than the sides.
- Syllables and words. The new sound is practised in simple syllables, then in words at the start, end and middle. Word lists at this stage are often chosen so the sounds nearby make the s easier.
- Phrases, sentences and conversation. The hardest part is using the new sound automatically. This stage takes repetition over weeks or months, with home practice between sessions.
- Carry-over. The child monitors their own speech in real life, at school and with friends.
How long this takes varies with the child’s age, the type of lisp, how often practice happens and whether there are other speech differences. Many children make steady progress once the clear sound is established, but no clinician can promise a timeline.
What you can do at home
- Model, do not correct. If your child says “thun”, answer naturally using the word: “Yes, the sun is bright today.” Hearing the clear sound in conversation helps more than being asked to repeat it.
- Get hearing checked if there is any doubt, and ask your dentist about the bite if your child has an open bite or long-term thumb sucking.
- Reduce pacifiers and thumb sucking gently, with encouragement rather than punishment.
- Build sound awareness. Play “listen for the snake sound” with books and songs so your child notices s before being asked to produce it.
- Follow the SLP’s lead on practice. Once a clear s is established in therapy, short daily practice (5 to 10 minutes) makes a real difference. Our S word lists sort words by position in the word, and the articulation practice tool is set up for quick sessions. Practising before the child can make the sound correctly tends to rehearse the lisp, so wait for guidance.
- Keep it light. Praise the effort and move on after a few tries. More ideas are in our guide to speech therapy activities at home.
Getting an assessment in Ontario
If your child has not yet started school, you can self-refer to Ontario’s free Preschool Speech and Language Program. No doctor’s referral is needed. Once a child is in school, school board speech-language services are often consultative, and families with a lisp as the main concern sometimes choose private therapy, which OHIP does not cover but many extended health plans partly do. Our guides on when to see a speech-language pathologist and how to get speech therapy in Ontario walk through each route. If you are comparing sounds beyond s, the speech sound development chart shows the usual ages for all 24 consonants.
Sources
- ASHA Practice Portal: Speech Sound Disorders: Articulation and Phonology
- ASHA Practice Portal: Orofacial Myofunctional Disorders
- Crowe, K., & McLeod, S. (2020). Children's English consonant acquisition in the United States: A review. American Journal of Speech-Language Pathology
- Bowen, C. Table 1: Phonological processes (speech-language-therapy.com)
- Ontario Preschool Speech and Language Program
How this guide was written
Written by the Speechie team. Every clinical claim is tied to a published source listed above. Guides are reviewed when the underlying guidance changes and the date shown above reflects the last substantive update. This is general information, not individual advice, and not a substitute for assessment by a registered speech-language pathologist. In Ontario, families can self-refer to their local Preschool Speech and Language Program at no cost.